Re: [Qgis-user] GIS Institutes - Online Courses

[David Strip via QGIS-User]

  
  
On 4/13/2024 12:45 PM, krishna Ayyala
  via QGIS-User wrote:

I
  wish to enroll in some of the online GIS courses. Is there a place
  or weblink where can I get the complete list of GIS Institutes
  that offer online courses? I am looking for institutes that are
  located in the USA, Canada and Europe.

Coursera has quite a few from a range of US and Canadian
universities. Many are free, though you must pay if you want a
formal credential or credit.
  

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Re: [Qgis-user] [QGIS-Developer] Announce - migrate our mailing lists to Discourse

[David Strip via QGIS-User]

  
  
On 4/10/2024 9:00 AM, Régis Haubourg
  via QGIS-User wrote:

I also
  heard yesterday another argument, given that we have
  StackExchange, mailing list and forums would be of no use.  Except
  you don't discuss on StackExchange, you only ask questions. And we
  don't own the content (side remark) there.  

Stack Exchange is not a good substitute. A number of the most active
users are quick to close any post with more than one question, often
making it hard to coherently post about your issue.
  

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Re: [Qgis-user] Moving many project files - bulk updating paths to tables?

[David Strip via QGIS-User]

  
  
On 4/5/2024 2:15 AM, Antonio Viscomi
  via QGIS-User wrote:


  if you're using linux what you need is simply use the 'sed'
command by terminal as i.e.:
  
  
  sudo sed -i 's/NEWPATHTOSUBSTITUTE(your path or IP or
  domain)/OLDPATH/g' *.qgs


The original request noted that the files were .qgz files, not .qgs,
so you need to first unzip, the rezip the files.
And this single line solution assumes all files are in a single
directory, so you need something "find" to walk the directory
structure.
  

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Re: [Qgis-user] Announce - migrate our mailing lists to Discourse

[David Strip via QGIS-User]

  
  
I've never used Discourse so I'm not in a position to compare it's
usefulness to the existing email format. I can add one more voice
expressing satisfaction with the email approach and how it
encourages readers to view everything rather than narrowing focus to
topics of interest. It also strikes me that we will inevitably lose
some people in the transition because of the friction required to
move focus to a new format, regardless of whether you like or hate
Discourse.
  

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Re: [Qgis-user] How to create 3d terrain from DEM?

[David Strip via QGIS-User]

  
  
In addition to the advice you've already gotten, the reason your 3D
model is so "wonky" is that you don't have elevation data outside
the region you plotted, so these all have elevation zero.  Since the
region is around 8500' elevation, that creates the vast wall effect
you're seeing. 
More fundamentally, however, is that you are taking an unnecessarily
difficult path to creating this model. You can download a 1/9
arc-second DEM from the National Map
which gives you a highly accurate elevation model for the entire
region, eliminating the problem you're having. 
Contact me off the mailing list if you want more help.
 
  

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Re: [Qgis-user] Hillshade default direction

[David Strip via QGIS-User]

  
  
Thank you to both of you for your informative responses. 
This prompted me to look at some satellite imagery and while the
plateau vs. valley effect is not as distinct, the reversal of hills
persists. Never noticed that before.
  

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Re: [Qgis-user] Convert PNG file to vector file

[David Strip via QGIS-User]

  
  
On 10/25/2023 7:46 AM, krishna Ayyala via QGIS-User wrote:

  
  
Thanks for the reply Simon. The
Polygonize tool did not work for me.

  
Regards.

  

It's not surprising that polygonize didn't work. Polygonize
recognizes regions of constant color. The patterned fills of the
regions in your file will completely defeat polygonize. The fact
that regions overlap only further complicates the matter. You will
either have to manually digitize the image or find someone who has
the files that were used to generate the map.
  

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Re: [Qgis-user] Pro tips for beginners

[David Strip via QGIS-User]

  
  
Another "pro" tip (from a non-pro) - 
  Create keyboard shortcuts for frequently used commands, such as
  this one suggested by Michael Duffy - 
  

-Copy and paste styles
between layers.


  

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Re: [Qgis-user] Problem saving project to geopkg

[David Strip via QGIS-User]

  
  
On 7/25/2023 11:55 PM, Michael Dufty
  wrote:


  The
  error message includes MedicalDebt.mldata as a project name. 
  I believe this is the file the memorylayer saver plugin
  creates to save the temporary layers to.   Have you tried it
  with that plugin disabled?  
   
  I'm
  really dependent on the memory layer saver plugin, and have
  abandoned investigation of saving files to geopackage because
  memorylayer saver does not seem to support it.


the problem appears not to be the presence of the memory layer
plug-in specifically, but the combination of the plug-in and a
memory layer in the project. If I have a memory layer open in the
project when I try to save to a geopkg, I get the error. If I remove
the memory layers (or save them to the geopkg and replace the memory
layers with the saved layers), then the problem disappears. 
  

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[Qgis-user] Problem saving project to geopkg

[David Strip via QGIS-User]

  
  
I created a geopkg by exporting a layer from my project to a new
geopkg. I then exported a couple of other layers to the geopkg. I
then did File->Save To-> geopkg and saved my project to the
geopkg. So far, so good. Now I made some changes to the project and
tried to save it and now I get a python error 
ValueError:
Cannot open
geopackage:C:/Users/David/Documents/Geodata/Maps/RIP_Medical_Debt.gpkg?projectName=MedicalDebt.mldata
  
How do I fix this?
Thanks



  

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Re: [Qgis-user] Problems with QGIS 3.28

[David Strip via QGIS-User]

  
  
On 7/11/2023 11:41 AM, John Studley via
  QGIS-User wrote:


  Please can someone help
  
  
  QGIS 3.32 will not install on my Windows 10 - I am told that
various files are missing
  QGIS 3.28 will install but the layer box is too big so I
cannot change the polygon colour rendering
  QGIS 2.12 will install but I cannot add plugins but I can
change polygon colours
  
  
  Today I wanted to publish a map on the QGIS cloud so I had to
  1) edit polygon colours in 2.12
  2) Uninstall 2.12
  3) Install 3.28 
  4) Add the requisite plugins
  5) Publish map in cloud
  
  
  There has to be a better way


We need to know which installer you're using to help and at least a
partial list of the missing files.
If you install using the OS4Geo network installer, you can have
multiple versions installed at the same time, so you would not need
to uninstall 2.12 before installing 3.28.

  

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Re: [Qgis-user] QGIS controlling access in QGIS

[David Strip via QGIS-User]

  
  
Expanding on what Chris said - 
Qgis does not own or manage data, Qgis manipulates and displays data
from files, databases, and web services. As Chris points out, access
to files is controlled through OS settings, databases by database
settings. Web services may require authentication for access. When
Qgis is used to create derivative datasets, these will be stored in
a file system or database, again subject to the sorts of access
restrictions that these systems provide. 

On 5/30/2023 9:59 AM, chris hermansen via QGIS-User wrote:

  
  
Simon and list,
  
  
On Tue, May 30, 2023,
  08:48 Simon via QGIS-User 
  wrote:


  
Hello, 


It's
  me again, I just had some questions regarding the
  ability to control access in QGIS. First of all, is it
  even possible? Can an organization (like departments
  of the Canadian government) control who has access to
  which database or file? Can the IT department of that
  organization manage the access?
  

  



Access to files is controlled through operating
  system settings. Access to databases is controlled by database
  settings. Normally in organizations system administrators
  manage these settings.


Whatever software application is run is limited
  in its access by those settings. It would be unusual for an
  end user software application to further manage access.


Settings typically include ability to read,
  ability to write, ability create and ability delete. So for
  example a set of shape files could be shared as read only to
  users, to a group of users, or via access control lists.


To your point - access to resources is not
  controlled through QGIS; it is controlled by the operating
  system, and by the database server if one is used.

  

  


  

  

  
  
  
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Re: [Qgis-user] Issue with QgsLayerTreeNode.itemVisibilityChecked

[David Strip via QGIS-User]

  
  
On 5/22/2023 7:44 PM, Patrick Dunford
  via QGIS-User wrote:


  extentGroup = root.findGroup(extentGroupName)
  
  extentLayers = extentGroup.children()
  
  for extentLayer in extentLayers:
  
      if extentLayer.itemVisibilityChecked:
  
          print (extentLayer.name())


shouldn't that be 
 if extentLayer.itemVisibilityChecked():   
(note the addition of parens after the method name).
  

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Re: [Qgis-user] [EXTERNAL] Re: Geopackage slow on NAS if not read-only

[David Strip via QGIS-User]

  
  
On 3/18/2023 1:50 PM, Patrick Dunford
  via QGIS-User wrote:

but I
  use NFS, which is not available on Windows (my computers run
  Linux)

NFS is available on Win 10 and 11 in the Pro and Enterprise
versions, but not the Home version.
I think it is not on by default, however.
  

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Re: [Qgis-user] Formatting dynamic text

[David Strip via QGIS-User]

  
  

  I am trying to use the dynamic text option  [%item_variables('Map
1')['map_scale']%] in my print layout but I get a scale of 10.7
in my title block. How can I apply a format number to get it to display a
whole number like 10?


I don't know how to do it using dynamic text, but you can get what
you want using this _expression_
[% round(map_get( item_variables('Map 1'),
  'map_scale'),0)%]
  

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Re: [Qgis-user] The theory behind topology

[David Strip via QGIS-User]

  
  
If you're asking the more general question about various geometric
algorithms (like intersection, union, inclusion, etc) you might want
to look at a text on computational geometry.
  

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Re: [Qgis-user] importing GeoPDF

[David Strip via QGIS-User]

  
  
On 1/10/2023 10:01 AM, JOE LEMONNIER
  via QGIS-User wrote:


  Is there a way or a plugin that allows me to import GeoPDF file such as USGS topos into QGIS as vectors? I’m using version 3.22.6 and trying to import with Layer>AddLayer>Add Vector Layer, but it gives a message “ Invalid Data…"
Thanks in advance,

Joe LeMonnier

Using Qgis 3.26 on WIndows 10 I just drag the USGS topo geoPDF onto
the canvas. I get a dialog asking which layers I want. I selected
all and the resulting Layers window shows  a large number of vector
layers plus the satellite image layer.


  
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Re: [Qgis-user] Offering QGIS installers through Windows store

[David Strip via Qgis-user]

  
  
This is an intriguing idea. In addition to providing a revenue
source, it has potential benefits to certain classes of users.
You've already identified the automatic updating feature, which many
people will no doubt find desirable. Another feature is the
legitimacy of installing from the MS Store. We periodically see
posts from users in a corporate environment who cannot update to
some version or another unless the IT gods have waved their wands
and blessed a particular release. I expect there are middle ground
environments that don't allow random installations, but will allow
installations from the MS app store, as MS does provide at least a
modest vetting of the content. By providing QGIS through the app
store we will simplify access for users in that environment. 


On 11/22/2022 1:19 PM, Anita Graser via Qgis-user wrote:
Hi,
  
  
  With QGIS functionality and user base constantly growing, the
  required
  
  maintenance also keeps increasing.
  
  To keep our project budget sustainable, we (the PSC) are
  considering
  
  investigating the possibility of offering a Windows installers for
  sale
  
  through the Windows store in addition to the free installers from
  qgis.org.
  
  
  This approach would follow the example of projects such as Krita
  
  (https://krita.org/en/download/krita-desktop/).
  
  It would give our users an additional low-threshold way to support
  QGIS.
  
  And - if I understand the Krita offering correctly - users will
  also get
  
  automatic updates when new versions come out which is a nice
  service.
  
  
  Of course, we will keep offering the free installers and using the
  store
  
  would be completely optional.
  
  
  If you have any experience offering software through the store,
  your
  
  insights would be very much appreciated since we are still at the
  early
  
  stages of exploring this option.
  
  
  Regards,
  
  Anita
  
  
  
  --
  
  Anita Graser
  
  Home: http://anitagraser.com
  
  Twitter: @underdarkgisMastodon: @underdark...@fosstodon.org
  
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Re: [Qgis-user] multiple csv file import

[David Strip via Qgis-user]

  
  
Starting with v2.1, ogr2ogr supports
  args X_POSSIBLE_NAMES, Y_POSSIBLE_NAMES which are strings with
  allowed wildcards (eg, Lon* ), or you can use field_1, field_2,
  etc to explicitly give the position of lat/lon.
  It's explained on the driver page. 
  This StackExchange
  post shows csv to shapefile conversion and included Windows
  command line syntax for looping over files in a directory.
  
  On 11/15/2022 12:58 PM, Hugh Kelley wrote:


  
David, this was my first thought when i saw this question
  as well.


however, I didn't look for very long but I haven't seen a
  way to tell ogr2ogr to read columns in a csv as the lat/lon
  and write those as points to the shapefile.  I generally write
  a csv to postgres as a non-spatial table and then process the
  lat lon columns with postgis. 



 Are there arguments for ogr2ogr that can do this?
  


  

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Re: [Qgis-user] multiple csv file import

[David Strip via Qgis-user]

  
  
You might consider ogr2ogr as an alternative approach. You can run
this from the command line allowing you to use shell scripts to
iterate through all your .csv files. There are also python bindings
for ogr2ogr if you're more comfortable with python than shell
scripts.

On 11/15/2022 9:59 AM, Salvatore Mellino via Qgis-user wrote:
Hello,
  
  
  thank you for your answer. I have many csv (about 100), so I need
  an automatic procedure. Maybe a python script...
  
  
  Il 15/11/2022 16:55, Nicolas Cadieux ha scritto:
  
  Hi,


Yes, you can do that very easily using QGIS.  Layer/add
layer/add delimited text layer.  Then just export the layer in
the format of your choice. You may need to convert the
coordinates in decimal degrees (ex 75 05 30.4 ->
75.0917800 ).


You can do this in Excel using =(A6)+(B6/60)+(C6/3600)+(D6/3600)
A= Deg, B= Min, C=Sec, D= Decimal Sec.  Then export to csv.


Nicolas



On 2022-11-15 10:08 a.m., Salvatore Mellino via Qgis-user wrote:

Hello,
  
  
  I would like to know if it is possible to import multiple csv
  files contained in a folder and to convert them in shapefiles
  (1 for each csv). All csv files are structured as "lat long
  value" separate by space and without any header line.
  
  
  Thank you for your help! Regards,
  
  
  Salvatore
  
  

  



  

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Re: [Qgis-user] Updating QGIS version

[David Strip via Qgis-user]

  
  
Most Qgis installers for Windows do not do an update in place.
Instead they install an additional version of Qgis. This allows you
to keep running an earlier version of Qgis at the same time as the
newer one. This might be helpful in some cases, but because it's
atypical of most Windows programs, it is confusing the first time
you encounter this. The desktop or taskbar icon for your previous
version remains connected to the old version. You have to create a
new shortcut to access the new version. Once you are satisfied that
the new version hasn't broken any functionality you need, just go
ahead and uninstall the old version and delete any shortcuts you
have created.
Beware that in some cases a newer version of Qgis will write a
project file that is not backwards compatible. If you open an old
project, you will be warned that saving it will render old versions
unable to open it.

On 10/27/2022 2:40 PM, Sebastian Gutwein via Qgis-user wrote:

  
  I find that windows will open the version I
installed but continue to say the previous version when I open
it by searching windows. In  my case it says 3.18 but opens
3.26. Could this be happening to you? 
  
  
  
On Mon, Oct 24, 2022 at 4:40
  PM krishna Ayyala via Qgis-user 
  wrote:


  Hello,
I have QGIS 3.20 version. I was planning on updating to
  the latest version without uninstalling the current
  version. I have downloaded and installed  "OSGeo4W
  Installer" from the following webpage. The QGIS did not
  update to 3.26 version. My QGIS is still 3.20 version. Can
  anyone please help me fix this?

  

  

  

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Re: [Qgis-user] Fwd: Your message to Qgis-user awaits moderator approval

[David Strip via Qgis-user]

  
  
your best bet is to upload your screenshots to an image server (eg,
Imgur), then inline the images into your email.

On 10/7/2022 11:25 AM, Hugh Kelley via Qgis-user wrote:

  
  
Hi, 


I included a few screenshots in an email to the
  list and as a result it exceeded the acceptable file size. Is
  this something that can be approved or should I resend a
  smaller email? 
  



  

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Re: [Qgis-user] Problems with raster layer in geopackage

[David Strip via Qgis-user]

  
  
Starting with a tiff hillshade 10,812 x 10,812 8-bit unsigned int, 1
band , then exporting 

geopkg, default settings - 32,136K bytes
geopkg, manually setting TILE_FORMAT = PNG - 80,572K bytes
gtiff, default no compression - 114,287K bytes
gtiff, high compression (DEFLATE, predictor = 2) - 86,816K bytes

The default is still lossy as expected as the issue has not been
resolved, but it is possible to override the defaults by providing
the TILE_FORMAT = PNG options.



On 9/22/2022 10:36 PM, Nicolas Cadieux wrote:

  
  Hi,
  
I would test but it looks like the issue has not been
  fixed.
  
  Nicolas Cadieux
https://gitlab.com/njacadieux
  
  
Le 22 sept. 2022 à 23:36, David
  Strip 
  a écrit :
  

  
  

  
  On 9/22/2022 7:38 PM, Nicolas
Cadieux wrote:
  
  I
would not store raster in a geopackage unless it’s just
a pretty picture.  The default compression for that
format is not lossless.  I would just save as a .tiff. 
  If I use Properties->Export and export to a geopkg and
  add TILE_FORMAT to PNG, do I get a lossless export?
  (I saw this option in issue
40425 that you submitted back in 12/20.)

  

  


  
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Re: [Qgis-user] Polygon next to road search term

[David Strip via Qgis-user]

  
  
My starting approach would be to take the road layer and buffer that
out by some small distance - say 5 meters. (Note that you have to be
working in a projected coordinate system for the buffer distance to
have useful meaning.) I would then intersect the buffered layer with
the polygon (lot) layer. The resulting intersections will be the
overlaps between the buffered roads and the polygons. The attribute
table will contain a list of all the intersections and each row of
the table will contain the attributes of both the lots and the
roads, so if the lots and roads have attributes with meaningful
names, you will have a list of all lots that intersect roads and the
names of the road it intersects with.

You could also try extract by location from the processing toolbox.
This would give you a layer of the original lots (polygons) that
intersect some road, but won't tell you which road.

On 9/13/2022 10:19 PM, Jon via Qgis-user wrote:

  I would want the polygon to have road access. So you should be able to
access the polygon firectly from a road. Just a corner touching may
work but that would depend on an easement and I am having enough
trouble just trying to figure out what I should be searching on without
throwing that in as well.

So at this point, the polygon should be able to be accessed by the road
line. So possibly 20' of the road line is touching the polygon.

-Original Message-
From: David Strip 
To: j...@destar.net, Qgis-user@lists.osgeo.org
Subject: Re: [Qgis-user] Polygon next to road search term
Date: Tue, 13 Sep 2022 21:12:01 -0600

  Is a polygon "next to a road" because one (or more) edges of the polygon is exactly coincident with the road line? Or is it within some distance of the road line? These lead to different solutions, but unless your data is very precise, asking for the boundary to be exactly coincident with a road line is not going to be very robust.Does your road polyline feature have a road width? If so, does that factor into "next to"?
 
 
 On 9/13/2022 5:26 PM, Jon via Qgis-user wrote: 

  
I am trying to figure out if a property that is a polygon is next to a
polyline (road). I am not well versed with QGIS and every search I do
seems to tell me how to map a polygon onto a road or convert polylines
to a polygon. I am not sure what exactly I need to search on to find
some documentation on how to do what I am looking to do.

What should I be searching on to find if a property that has 4 sides
and is a polygon is next to a road? Is what I am trying to find called
something specific and that is why I am not finding?

Thanks for any help,

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Re: [Qgis-user] Polygon next to road search term

[David Strip via Qgis-user]

  
  
Is a polygon "next to a road" because one (or more) edges of the
polygon is exactly coincident with the road line? Or is it within
some distance of the road line? These lead to different solutions,
but unless your data is very precise, asking for the boundary to be
exactly coincident with a road line is not going to be very
robust.Does your road polyline feature have a road width? If so,
does that factor into "next to"?


On 9/13/2022 5:26 PM, Jon via Qgis-user wrote:

  I am trying to figure out if a property that is a polygon is next to a
polyline (road). I am not well versed with QGIS and every search I do
seems to tell me how to map a polygon onto a road or convert polylines
to a polygon. I am not sure what exactly I need to search on to find
some documentation on how to do what I am looking to do.

What should I be searching on to find if a property that has 4 sides
and is a polygon is next to a road? Is what I am trying to find called
something specific and that is why I am not finding?

Thanks for any help,

Jon
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[Qgis-user] Problems with raster layer in geopackage

[David Strip via Qgis-user]

  
  
I have a geopackage called GMU5ab. I also have a map project called
GMU5ab, which is stored in that geopackage. With the GMU5ab project
open in QGIS,  I created a hillshade layer, called "Hillshade" in
the layer list. I saved this layer to the geopackage. Unlike a
vector layer which is stored with the legend name, the layer in the
geopackage was stored as GMU5ab and has a raster icon. If I right
click on a vector layer in a geopackage in the browser, I have the
choice of Manage->Rename Layer, but if I right click on the
raster layer, Manage only offers delete.

Is there a way to store the raster layer with the correct name in
the first place using Qgis?
Once stored, is there a way to rename a raster layer in a geopackage
from within Qgis.

QGIS 3.26 on Windows 10

Thanks


  

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[Qgis-user] Location of Layout with multiple maps.

[David Strip via Qgis-user]

  
  
It appears that if one creates a layout with multiple map frames in
the layout, then exports to GeoTiff with world file, the world file
will reflect the first map frame added to the layout, regardless of
where the frame is in the item stack (visibility order) or where it
is located on the page. Can this behavior be counted on?

(Obviously it makes no sense to think there could be more than one
location/world file, so that's not the issue). 


  

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Re: [Qgis-user] Tectonic plate boundaries

[David Strip via Qgis-user]

  
  
This page
contains a number of shapefile links and some KMZ links as well.

On 8/13/2022 10:37 AM, John Moyle via Qgis-user wrote:

  
  Hi
New to QGIS. I want to plot Victorian submarine telegraph
  cable interruptions under the Atlantic.  I know, what an
  Anorak!!
I have found a brilliant rasterfile of the seabed from
  GEBCO to use as a base layer. I have also collected all the
  data of cable failure, submarine earthquakes and volcanoes and
  am ready to make vector layers of all the data.
But what I can't find is a shapefile of the tectonic plates
  boundaries, just the boundary lines with no shading or text.
  Everything I do find is rejected by QGIS as not being in a
  suitable format.
Help please!
John
  

  
Dr
John Moyle
MB,
  BS, MSc, PhD, CEng, MInstMC, FRCA, FRHistS
Chartered
  Engineer
Physician
  & Anaesthetist (Retired)
Historian
  (Telegraphy & Medical Technology) 
  
  Home
+44(0)1608 665968
  Cell
    +44(0)7836 244584
  
  Amberley
  Cotswold
Close
  Tredington
  Shipston
on Stour
  Warwickshire
  CV36
4NR, UK 
  
  "A
person has nothing to lose if he believes
in God and in the end he turns out to be wrong but
everything to lose if he
wagers that God does not exist and it turns out in
the end that He really
does." - Blaise Pascal (C17th French Scientist &
Mathematician)
  

  

  
  
  
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Re: [Qgis-user] excessive threads?

[David Strip via Qgis-user]

  
  
On 7/30/2022 6:36 PM, Greg Troxel via
  Qgis-user wrote:


  
I do understand that threads could help parallelization, eitehr using
multiple cores, or just allowing IO in parallel.

chris hermansen  writes:



  Does it seem like you have one thread per layer for reading plus one for
rendering plus one for user  input?


I don't know how many layers I have :-)I can experiment with some
smaller projects.

When I noticed this, I had not tried to use qgis in at least a day.



  

I did a little bit of quick experimentation using Qgis 3.26 (Buenos
Aires) on Windows 10. The number of threads is all over the place.
It does not seem to be tied to the number of layers in the map, at
least in the sense of steady state (ie, let the app sit idle for a
while). Adding layers bumps the thread count, with shapefiles adding
more threads than files in a geopkg. Locally stored geotiffs are
more like a geopkg vector file in terms of threads. But once things
settle down I end up around 20 threads. Interestingly,
Help->About bumped the thread count by 8. Closing a project (not
saving) and then opening a "new" project (no template) bumped
another 8 threads for about 30 seconds, then settled back
down.Launching Qgis peaked at 30 threads, then after about it minute
settles down to 14. I suspect this is dependent on which plug-ins
I'm running. 

Note these numbers are non-deterministic - Help->About on a fresh
start of Qgis with an empty project jumped from 13 threads to 33,
then settled down to 22, which is different from the previous
attempt where there were open layers in the map.

I'll be interested to hear what drives the thread count to > 150
. None of my very limited test involved database connections or
connections to remote data. Those might have something to do with
it. Maybe layer filters? Complex rendering (eg, geometry
generators)?
  

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Re: [Qgis-user] Convert huge shapefile to small size

[David Strip via Qgis-user]

  
  
On 7/28/2022 5:52 AM, krishna Ayyala via Qgis-user wrote:

  
  dbf file itself is 5.1GB. Rest all other files are
less than 500MB. It is the number of records which is huge. It
has about 117,2100 points.
  


Is that 117,200 points or 1,172,100 points? In either case, there's
almost certainly  something wrong with your file, as you have either
50K or 5K bytes per point, which is off by one or more orders of
magnitude.

For comparison, I created a set of 1M random points with 14
attributes inherited from the polygon they lie in. This includes 3
qlongong fields, 9 doubles,  and 3 strings with a total length of 40
chars. I saved this as a shapefile and the total size is ~300M.
  

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Re: [Qgis-user] copy and paste very slow in qgis

[David Strip via Qgis-user]

  
  
On 7/4/2022 9:03 AM, Michael.Dodd via
  Qgis-user wrote:


  I am trying to copy points with their
attributes from one layer to another (actually one geopackage
file to another), the select is quick, couple of mins, bearing
in mind there are 800,000 points but when pasting into the new
empty geopackage file it is extremely slow. Less than 10% of the
points need to be pasted but it was taking 40mins before I
stopped it and I had no idea how much longer it would take.
There was a hint that it may have done about 30,000 in 40mins.
  Is there another way to do this, I have also
tried switching the selection and deleting the other 90% but
this too is very slow and don’t see the end.

Have you tried selecting the features, then Export->Save
Features, ticking Save Only Selected Features?
  

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[Qgis-user] saving styles to geopackage

[David Strip via Qgis-user]

  
  
I know that I can style a layer and save the style to a geopackage.
In doing so, I associate the style with the layer, but can retrieve
that style later for use on a different layer.
Is there any way to create a geopackage of "bare" styles - styles
not associated with a particular layer, just a catalog of styles. 
For example, let's say I'm creating a suite of topo maps and I want
the various layers of each map styled consistently. I could fetch
the styles from a geopackage in which the style has been connected
to a particular instance of the the layer type, but it seems it
might be nice to just have a catalog of styles in a geopackage. I
can do this outside the geopackage system by storing qml files in a
directory, which is fine, but a geopackage feels neater. 

  

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Re: [Qgis-user] Dimensioning in QGIS

[David Strip via Qgis-user]

  
  
On 6/25/2022 6:43 PM, Richard Greenwood
  wrote:


  
  
  At the risk of stating the obvious, all of that can be done
with labels in QGIS. A simple line can be annotated with angle
and distance, which are dynamically updated when the line is
modified. QGIS has the ability to move labels relative to the
object being labeled and supports "call outs" aka "leader
lines". Labels are not "model objects", in other words, labels
are saved in the QGIS project, not in the underlying data. 


This is certainly true - it's just a question of how hard it is to
accomplish.
Here's an example - starting with a polygon layer, I want
to dimension two boundaries of my property - 

I claim no particular expertise in this, so here's my process - 
Convert polygon to lines
explode lines
delete lines that I don't want labeled
use the geometry
  generator provided earlier in this thread
tweak half a dozen parameters buried in the geometry generator to
get the styling I want. 

If users are going to want to routinely add dimensions like this, it
would be far preferable to extend the annotations system to include
a linear dimensioning tool that just requires mouse clicks on two
points and a basic styling dialog. 



Please note that I am not particularly advocating for adding
dimension capabilities to Qgis, as I personally have no use case and
don't know whether there is a common enough need to warrant the
effort. However, I do have extensive CAD experience and was trying
to translate the CAD terminology to the GIS folks unfamiliar with
what "dimension" means in the CAD world, as there seemed to be a lot
of questions about the meaning. 


  
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Re: [Qgis-user] Dimensioning in QGIS

[David Strip via Qgis-user]

  
  
To the extent that anyone is interested in a discussion of adding
CAD-like dimensioning capabilities to Qgis:

In a CAD model dimensional callouts present the user with
information about lengths, angles, radii, and other metric
properties. Dimension call-outs  in a CAD model (probably more
accurately, a CAD drawing derived from a model) are annotations to
the model, they are not model objects per se. In a well-designed
system, the dimension call-out displays the actual metric value of
identified length, radius, angle, etc. The dimension "object" is
tied to the underlying geometric model and will change the presented
value if the underlying object is changed (eg, scaled in size). In
addition, if the underlying object moves with respect to other
objects in the model, the dimension annotations move with it,
maintaining a constant relationship, for example to the edge whose
length we are dimensioning. 

Extending this notion to GIS in general, and Qgis, introduces a bit
of a difficulty in the sense that CAD systems tend to have a fuzzy
boundary between the notion of what in Qgis is the map canvas and
the  a layout. Sketchup, a popular (and free-ish) CAD modeler allows
dimension annotations in what amounts to the canvas, but also has an
adjunct program Layout for drawings, much like a layout in Qgis. 
That said, I would suggest the starting point in Qgis would be an
annotation capability in the canvas, much like the annotations
introduced in 3.22.  When adding a dimension to the canvas, a user
would click on some aspect of a feature, typically a vertex or other
point-like feature, then click on a second, and a line/arrrow would
be added as an annotation, with text indicating length. Things get a
little more complicated trying to dimension the radius of a circle,
as these are represented in different ways depending on the data
format (eg, shapefile vs. geopackage). To match the semantics of CAD
dimensions, the stored representation would be tied to the
properties of the feature, not to the geo-referenced value at the
time the annotation was created so as to allow the dimension to
dynamically respond to changes in the underlying data. 

None of this gets to the question of should this be added? There are
important differences between a CAD model and a map. A CAD system is
used for design, just as the name says. A CAD model generally goes
through a series of revisions over it's lifetime. A map (at least
for me) is generally intended to reflect a physical reality. It may
experience changes as we refine our understanding of the underlying
physical reality, but in general maps tend to reflect data that is
far more static than that in a CAD model. This suggests that perhaps
we really don't need the same sort of dynamic dimensioning
capabilities that a CAD system provides. WIth that in mind, I think
the appropriate starting point for dimensioning in Qgis, if we want
one at all, is to add a "linear dimension" tool to the existing
annotation toolbar. The tool would allow the user to snap a line
between any two vertices (or points) on a layout, and would add a
dimension arrow between the two points, and perhaps extension
lines,  labeled by default with the appropriate distance. Until a
more compelling use case presents itself, I think it would be
sufficient to make the new dimension annotation be statically
geo-referenced. 
  

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Re: [Qgis-user] Dimensioning in QGIS

[David Strip via Qgis-user]

  
  
although a CAD drawing may be drawn to some scale, it is common to
explicitly label lengths (distances) using arrows and extension
lines.



I suspect the OP wants to create dimensional arrows labeling
distances between features on the map, eliminating the need to
measure a scaled distance (say on a printed map), then multiplying
by scale factor, which is almost sure to introduce inaccuracy, as
well as inconvenience.

On 6/23/2022 5:23 PM, Greg Troxel via Qgis-user wrote:

  IainS via Qgis-user  writes:


  
Is there a tool for adding dimensions in QGIS. For those who are wondering
what I am talking about, it is common in CAD drafting to add dimensions to
what you have drawn and this is a whole part of a CAD program where you can
format dimensions .etc.

I have been asked to add dimensions to an archaeological hole I am digging
on a QGIS map and I was wondering whether there is a similar dimensioning
tool in QGIS.

  
  Can you explain what you mean without saying "like CAD"?
Distances are or can be in meters, and it is normal to have a scale on
a map.  So I don't know if this is about representing length
conceptually or about labels with lengths, or ?

Perhaps a link to what you have and what the specific complaint is would  help.

  
  
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Re: [Qgis-user] polygon fills from different shapefiles

[David Strip via Qgis-user]

  
  
On 6/21/2022 8:37 AM, Firstname
  Lastname via Qgis-user wrote:


  I have gone that far, but I have four sets of maps
with similar units.  If I categorize them independantly, I have
to manually change the colours to make them consistent between
layers.   This is very time consuming and I was wondering if the
colour can added to the attribute table so that I can edit them
more easily 
  

  On Tue, Jun 21, 2022 at 2:56
AM 
wrote:
  
  

  
Context menu of your shapefile > properties >
  choose Tab "Symbology" > select "Categorize" in the
  first line with the attribute for the name of the
  geologic formation as the value in the second line.
  Click on "Classify" and style your polygons as
  appropriate.
 
Regards, Christine
  

  

  


Assuming all the shapefiles use the same name for the attribute you
will use for categorization, you can save the styling to a style
file from the Symbology tab of the Properties dialog. Do this once,
then load the style file to the other layers.
  

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Re: [Qgis-user] Problem trying to graduate by value (colum)

[David Strip via Qgis-user]

  
  
A lot of folks get bitten by text fields that look like numbers.
What if the attribute table color-coded the columns with different
colors for text vs. numbers? Or had a second row of headers showing
the field type? What would the disadvantage of such an approach? Of
course, the color coding/field type could be optional.

  

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Re: [Qgis-user] How to specify buffer distance in Metres when Using WGS84 (EPSG:4326) geometry.

[David Strip via Qgis-user]

  
  
On 3/21/2022 1:44 PM, Bernie Connors
  via Qgis-user wrote:

 
        I am using QGIS 3.20.0-Odense and I have a small set of
  points in EPSG 4326, a geographic projection.  I am trying to use
  the Multi Ring Buffer tool and the units for the buffer distance
  is in "degrees" but I want to specify a buffer of 5 metres.  The
  tool doesn't appear to allow me to change the units for the buffer
  distance.  What can I do here?

You have to set your project CRS to a projected coordinate system in
meters. (Strictly speaking it could be in something else like feet
or miles, but you would have to manually convert the meters to the
units of the CRS). 

  

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Re: [Qgis-user] again: Create Geospatial PDF producing faulty output

[David Strip via Qgis-user]

  
  
On 3/21/2022 9:52 AM, Ken Sanderson via
  Qgis-user wrote:

If TIF
  output is spatial and is working fine, print to that, then use
  gdal to convert that to pdf?
This would result in a pdf that is nothing more than a bitmap. It
would lose the layer structure that a vector pdf can contain.

  

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Re: [Qgis-user] Browser and Layout side bars now hidden

[David Strip via Qgis-user]

  
  
On 3/13/2022 8:27 AM, Mike Breiding - Morgantown WV via Qgis-user
wrote:
Greetings,
  
  I have somehow made hidden the Browser Layout and side bars and
  now only the canvas is visible.
  
  What must I do to have them visible again?
  


From the main menu bar -
View->Panels (near the bottom of the list)
Then tick the browser and layer checkboxes
  

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Re: [Qgis-user] Automating creation of county distribution maps

[David Strip via Qgis-user]

  
  
As first step towards building a model as Nicolas has suggested:
I assume you have a layer with the county boundaries. Export this
layer as a CSV file, keeping only the name of each county in the
export step, and don't export the geometry.
Now open this file in your spreadsheet app of choice.
Add a new column for each plant species.
Put a one in that column for each county where the species is
present.
Save the file (still as CSV).

Open the county layer and the new CSV files in Ggis.
Open the properties window for the county layer and click on the
Joins tab.
Click on the "+" to add a new join. Join to the CSV layer, and
select the county names field as the join field for each.

Now your county layer has the plant species column.
To display a single species, open the properties window for the
county layer, select symbology. Set the symbology as rule based. To
color just those counties with species 1, your rule would say
something like Species1 = 1, where Species1 is the field name you
used. Pick a color/transparency of your choice, then set the "all
others" rules to be the background color you want.

That does it for one species. You can then export to tiff or
whatever. Getting it to cycle through all the different species is
for someone else to explain.
  

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Re: [Qgis-user] Fwd: Your message to Qgis-user awaits moderator approval

[David Strip via Qgis-user]

  
  
On 3/8/2022 11:04 AM, Cory Albrecht via
  Qgis-user wrote:


  
  
  Could a
moderator deal with this, please? It's been sitting for a few
days. I attached some images to explain my problem. Thanks in
advance.


you could always just upload your images to some hosting service
like imgur or a cloud drive (google drive, OneDrive, etc), then put
links in your email. That avoids the need for the moderator to
intervene,
  

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Re: [Qgis-user] Rounding off QgsPointXY

[David Strip]

  
  
I'd start by building the array of values using just the rounded x,
y, and complex value, not storing a QgsPointXY. Something like

triplets =
[]
for point in points:
    # point consists of a QgsPointXY and a complex value -
[QgsPointXy, complex_value]
    triplets +=  [(round(point[0].x(), 3), round(point[0].y(),
3), point[1])]

#sort points by y value
triplets.sort(key = lambda point: point[1])
# sort points by x value. Sort is stable, so now we have sorted
by x as primary, y as secondary

#walk the list of points looking for points with same rounded
value, summing complex value, outputting a new point when x or y
doesn't match
complex_sum = 0
last_x = triples[0][0]
last_y  = triples[0][1]
output = []
for t in triplets:
    if ((t[0] == last_x AND t[1] == last_y)):
        complex_sum += t[2]
    else:
        output += [(last_x, last_y, complex_sum)]
        last_x = t[0]
        last_y = t[1]
        complex_sum = t[2]


at the end of the loop the var output is a list of triplets (x, y,
complex) with the third element equal to the sum of the the complex
value for all points with the same rounded coordinates. 
I haven't actually tested, this so there could be errors. But the
idea is there.
There's probably a more pythonic way to do this, but possibly harder
to read. 


On 2/20/2022 7:07 AM, Asim al-sofi wrote:

  
  Thank you for your reply
The issue I have is  that I have an array of values. each
  value consists of xy coordinates of a point and a complex
  value.
What I want is that the points that have the same xy
  coordinates to be added together(i.e,, their complex values
  need to be summed up)
Because of the high number of decimals of each point,
  sometimes a point like QgsPointXY(6500.1149100023632
  0), 0.25+0.25j] and a point like
  QgsPointXY(6500.1149100023631 0), 0.25+0.25j] would
  be considered as two different points.
Thanks in advance
Asim
  
  
  
On Sun, Feb 20, 2022 at 5:21
  AM David Strip <qgis-u...@stripfamily.net>
  wrote:


  
On 2/19/2022 6:03 PM, Asim al-sofi wrote:

Hi everyone
  I have a problem rounding off the QgsPointXY to say 3
decimals? How can I do that?
  If I use the numpy.round(point,decimals) then I get
an np.array back as a type and not a QgsPointXY.
  Can someone help?
Kind regards
  Asim


what are you trying to achieve? Keep in mind that in general
decimal fractions do not have exact representations in
floating point, so if you round a coordinate to 3 decimals,
store it somewhere, then print it, there will almost
certainly be more than three numbers past the decimal point.
If it's the printed representation of the number that
matters, deal with it in the formatting of the printed
representation.

That said, you set() method of QgsPointXY to set the values
to their rounded values. If my_pt is a QgsPointXY, then

    my_pt.set(round(my_pt.x(), 3), round(my_pt.y(), 3))


  

  


  

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Re: [Qgis-user] Rounding off QgsPointXY

[David Strip]

  
  
On 2/19/2022 6:03 PM, Asim al-sofi
  wrote:

Hi
  everyone
  I have a problem rounding off the QgsPointXY to say 3
decimals? How can I do that?
  If I use the numpy.round(point,decimals) then I get an
np.array back as a type and not a QgsPointXY.
  Can someone help?
Kind regards
  Asim


what are you trying to achieve? Keep in mind that in general decimal
fractions do not have exact representations in floating point, so if
you round a coordinate to 3 decimals, store it somewhere, then print
it, there will almost certainly be more than three numbers past the
decimal point. If it's the printed representation of the number that
matters, deal with it in the formatting of the printed
representation.

That said, you set() method of QgsPointXY to set the values to their
rounded values. If my_pt is a QgsPointXY, then

    my_pt.set(round(my_pt.x(), 3), round(my_pt.y(), 3))


  

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[Qgis-user] QGIS at The Economist magazine

[David Strip]

  
  
This
  article has an interesting discussion on the use of
projections in news graphics and cites Qgis numerous times as their
mapping software.
It also mentions projectionwizard.org, which I was not familiar with
and is a useful to know about.

  

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Re: [Qgis-user] add Google Biking Layer to QGIS

[David Strip]

  
  
I could be reading the code wrong, but the link you sent is not a
leaflet map. It's a Google map, served directly from Google.

On 1/17/2022 11:28 AM, Hugh Kelley wrote:

  
  
Hi all, 



I'm wondering if anyone knows a way to add Google's bike
  layer to a QGIS map using the google map _javascript_ api. 



I believe that the layer is vector not tiles


here's an example of how to add it to a leaflet map so it
  does seem possible to use it in QGIS but it's unclear to me
  whether there is a feature or plugin to work with this sort of
  datasource rather than adding it in with python. 





https://developers.google.com/maps/documentation/_javascript_/examples/layer-bicycling




Thanks for any suggestions!





-- 

  

  

  
Hugh Kelley       
  
  

  

  

  

  
  
  
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Re: [Qgis-user] HTML Image Map

[David Strip]

  
  
On 1/7/2022 9:45 AM, Johannes Kröger
  (WhereGroup) wrote:

Aww,
  I loved that plugin so much. For so many use cases people don't
  actually need a zoomable, movable map with controls and tiles and
  _javascript_ and all that. The image map gives some low resource,
  pixel perfect, easy UX, independent solution. A real underdog in
  modern webdesign! Maybe I will fix it up for QGIS 3 some day.


Amen to the "low resource" part. It's amazing how often our tech
masters forget that we don't all live on the end of massive fat
pipes. 
  

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Re: [Qgis-user] Disassemble GPX files

[David Strip]

  
  
You can probably do this with GPSBabel.
GPX files are just XML files, so some sort of general XML utility
could probably do it as well.

On 1/3/2022 12:30 AM, APM wrote:
Dear Qgis-user,
  
  
  
  I have a lot of gpx-files, which contain several tracks each.
  
  
  
  Is it possible to disassemble this files in several files in a
  batch, which contain only one track each?
  
  
  The file name should be the  tag of the track.
  

  

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Re: [Qgis-user] mapping bus routes

[David Strip]

  
  
For a transit map, it seems the offset would not be constant.
Consider two bus routes that overlap along a single street in their
routes. On that street, the two lines typically would be offset to
opposite sides of the line representing the street. On the rest of
the route, however, the route would be shown as lying directly over
the centerline, not offset to either side. Life gets even more
complicated when multiple routes overlap with different numbers of
other routes at various points on the map.  Or at least that's what
I've typically seen on transit maps. 

On 10/7/2021 3:30 PM, Nicolas Cadieux wrote:

  
  Hi,
  You can also trim the lines in the symbology (at least in
QGIS 3.20) as well as giving it an offset.  That will insure
that intersection are not overlapping in the offset.

Nicolas Cadieux
  https://gitlab.com/njacadieux


  Le 7 oct. 2021 à 17:23, Nicolas
Cadieux  a écrit :

  


  

Oups!  Forgot the list…

Nicolas Cadieux
  https://gitlab.com/njacadieux


  Le 7 oct. 2021 à 17:23, Nicolas
Cadieux  a écrit :

  


  

Hi,
You can automatically draw an offset by adding a
  offset in the symbology.  Things get more complicated
  when line vectorization changes directions as the
  offset flips side depending on, for example, if the
  line is drawn from A to B or B to A.  


In the QGIS models, https://plugins.qgis.org/,
  go to models then Fix Directional Network models 1,2
  and 3.  That will help you find problems (like
  disconnected lines) but also identify all the lines
  that are flipped. You can then flip them manually or
  figure out an algorithm to do it automatically.


You will also find a boring YouTube video on my
  YouTube channel. https://youtu.be/v61PafSByvM
  
  Nicolas Cadieux
https://gitlab.com/njacadieux
  
  
Le 7 oct. 2021 à 14:17, Hugh
  Kelley  a écrit :
  

  
  

  
Hi all, 



I'm wondering if anyone has any good tricks
  for mapping bus routes. The key problem is
  defining how to offset lines where the routes
  overlap. 



I've handled this by chopping up the lines
  and offsetting in postgis according to some
  st_dwithins and st_intersections but wanted to
  see if there is anything in the wide world of
  QGIS that I'm not aware of. 



My understanding is that it's a fairly
  significant challenge to do a great job with
  it. A company called transitapp had an
  interesting blog post about it a while ago. https://archive.transitapp.com/transit-maps-apple-vs-google-vs-us-cb3d7cd2c362#.e9kcryzg1



  

  

  
Hugh 
  
  

  

  

  

  
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Re: [Qgis-user] Geo Raster Background

[David Strip]

  
  
When georeferencing, aren't the areas
  outside the original image, eg, the "triangles" resulting from
  rotation, treated as no data? Wouldn't this issue be resolved by
  setting the no data value to something other than black?
  Just guessing here, obviously.
  
  
  On 10/1/2021 2:36 AM, L.W. wrote:


  Thanks for answering, but I think this is not the way I want to
go ...
  Or, I do not have written detailed.
  
  I have a raster image e.g. a white rectangle, after setting the
points, QGIS rotats this image, let's say, by 45 degrees.
  The corners of the imported image are now black triangles.
  I do want to have e.g. red triangles ...
  Regards
  
  
  
  Am 01.10.2021 um 09:50 schrieb
Charles Dixon-Paver:
  
  

There's not really any way for a GIS system to
  automatically differentiate between black background pixels
  and black data pixels. QGIS supports users setting custom
  pixel values to render as transparent pixels, but it's left up
  to users to ensure that their data and background values are
  different.
  
  From my view, there are a couple of options when it comes to
  fixing this issue in your data. One is to use an image
  processing tool like GIMP or Photoshop effectively, but that
  requires retaining the geographic information and knowing how
  to reprocess the raster accordingly.
  
  The simplest solution I'm aware of is probably to follow this
  workflow in QGIS:
  
Start a new QGIS project
Set all black pixels to transparent in the transparency
  tab of the raster layer properties
Digitize a "bounding area" - you can do this with a
  memory layer
Move your vector layer to render underneath the raster
Give the vector a simple black symbology
Use the "Convert map to raster" tool from the processing
  toolbox
  
  There are a wide number of variations on that workflow
that are possible of course, but I think that's the easiest
to get started.

  


  

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Re: [Qgis-user] Point Shape file to Raster conversion.

[David Strip]

  
  
On 9/20/2021 7:16 PM, krishna Ayyala
  wrote:

Charles,
  Sorry for so many questions. As I mentioned before, I am able
to create georeferenced tiff file as per instructions in the
link below. But, when I overlay this tiff file on top of the
shapefile, the size of the points in tiff file is not same as
that of the size of the points in the shapefile. I tried to
export to tiff file with different resolutions, but that did not
work. Is there a way to fix that?
  
  
  https://imgur.com/a/soAI4E5


The shapefile contains coordinates; the points you see on the map
are how those points have been "symbolized". The default settings in
QGIS makes those symbols the same size regardless of the scale of
the map - as you zoom in or out the points remain the same apparent
size on your screen. When you  exported the map to a tiff, the
points became fixed in size. If you overlay the tiff on the original
at the same zoom level that you exported at, the symbols will
be the same size. As you zoom in or out, the symbols on the tiff
will appear larger or smaller on your screen, while the symbols for
the shapefile points will remain constant in apparent size. 

  

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[Qgis-user] Save map as image - setting scale/extent/DPI

[David Strip]

  
  
I can't seem to find an order for selecting scale, extent, and DPI
that allows me to select all three parameters, which should be
independent (or at least I think they should, if you allow hieght
and width to be the dependent parameter). If I start with "Draw on
Canvas" to select an extent, then select a map scale, the extent
changes, but the pixel count remains constant. If I start with the
scale, then "Draw on Canvas", the scale changes.
Same problem occurs if I set the extent via "Calculate by layer".
The output width/height get treated as independent inputs and are
held fixed. I do not have "Lock aspect ratio" set.

Am I doing something wrong, or is this a bug/misfeature? Has this
changed since 3.16.7?

I've been bothered by this for a while, but this
  GIS SE post prompted me to finally ask about this.

Thanks
David 

  

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Re: [Qgis-user] QGIS on a mobile platform

[David Strip]

  
  
On 9/10/2021 11:07 AM, Kirk Schmidt
  wrote:

Another
  option is to use Avenza Maps (commercial) to view your
  georeferenced pdf's directly on a phone or tablet. 
 The free version will allow you to download 3 non-store maps (ie,
maps you made) at a time. This will allow you to test suitability
before subscribing.
(or if you can live with the 3 map limit on any given device, you
don't need to subscribe at all.)

If you really want to stick to a Windows machine, Acrobat Reader
with the Terrago geo-pdf toolbar will read geo-referenced pdfs and
do simple actions like measurements.

  

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Re: [Qgis-user] QGIS on a mobile platform

[David Strip]

  
  
Again, not what you're asking for, but have you looked at the Avenza
Maps app, which runs on Android and iOS devices? It will display
your maps and if the device has a gps in it, also show location.


  

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Re: [Qgis-user] Problem with scale/magnifier

[David Strip]

  
  
On 9/7/2021 2:08 PM, Stewart Holt
  wrote:

Setting
  the scale at X and the magnifier at 200% behaves identically to
  the scale at X/2 and magnifier at 100%. 
While there may be issues with WMS layers (I don't use them often
enough to have noticed), it's certainly not true in general that
doubling the magnification is the same as halving the scale. In
particular, create a simple map with a layer with labels on. If you
halve the scale, the text on your screen remains the same size as
before. If you double the magnification, the text is twice is big on
your screen. Same goes for many aspects of symbology.

  

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Re: [Qgis-user] Line dissolve

[David Strip]

  
  
I looked at the source for this plug-in and as far as I can tell  it
only merges lines that meet at endpoints. It ignores multi-lines,
and only creates linestrings, so there are no vertices of degree
>2 (ie, no junctions/forks). Also, the plug-in doesn't look for
intersections between vertices (since it only looks to merge
endpoints.)
The StackExchange post appears to want multi-linestrings, which
gives forks and such. Is that what you need? 

On 8/30/2021 5:27 AM, Nicolas Cadieux wrote:

  
  Hi,
  This is the plugin I was referring to.  I don’t see it in the
current plugins (experimental turned on)  so I figured it’s QGIS
2 only.


https://github.com/ArMoraer/QGISMergeLines
  
  Nicolas Cadieux
https://gitlab.com/njacadieux
  
  
  

  


  

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Re: [Qgis-user] Default line width when importing data

[David Strip]

  
  
On Mon, 23 Aug 2021 at 02:27, Johanna Botman 
wrote:

  

  
The default is 0.26. I don’t know what
  unit of measurement that is, and it doesn’t really matter.
  I would just like to be able to set my own width as
  default.
  

  


.26 seems an odd number, esp. for a default. What's the origin of
this value?
  

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Re: [Qgis-user] Selecting Multiple Layers in a Single Click

[David Strip]

  
  
And here's a little selection oddity I've noticed. If you have a
layer with categories,  you can left-click next to a category (ie,
not the layer), then drag, you can drag-select a number of layers:




This only works if there are categories - if you try this on a
layer, you will move it in the legend order.
  

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Re: [Qgis-user] Need help with changing CRS

[David Strip]

  
  
I'm not sure exactly what you did, but I am a bit concerned by this:

  Then I changed the CRS (layer and project)

Try this:
Start with a new project
Add the Natural Earth Admin
boundaries layer
Select
File->Properties->CRS
Select Mollweide (or
whatever you want), then click Apply.

  
Note that we are not
touching the CRS for the layer.
  

  
I get a radically different
projection than WGS 84 (EPSG:4326).
  

On 8/17/2021 7:45 PM, Brian Gilhuly wrote:

  
  
  
  
I need a world map on
which to display country web statistics and, being in
Canada, want to avoid projections like Mercator with their
northern distortions. Something like Mollweide or Robinson
is more what I am seeking.
 
I downloaded the Natural
Earth administrative borders map (WGS84) and opened it in
QGIS 3.20 as the only layer in a new project. So far, so
good.
 
Then I changed the CRS
(layer and project) to Mollweide (ESRI:54009) and the
on-screen render changed hardly at all. It didn’t remain
unchanged, but it still looks very much more like WGS84 than
Mollweide. The same happens if I try to re-project to
Robinson (ESRI:54030) or Winkel-Tripel (ESRI:54042).
 
So far as I can tell, I
have followed all the steps outlined in the online manual
but there must be something obvious that I am missing.
 
Can someone set me
straight?
 
Thanks,
Brian Gilhuly
  
  
  
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Re: [Qgis-user] Layer Ordering for KMZ

[David Strip]

  
  
I tried your file on   Google Earth Pro 7.3.4.8248 (64-bit) on
Win10. I get an even stranger result - two of the small circles
appear on top of the big circles, the other two behind.
Both layers are listed as clamp to ground.



  

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Re: [Qgis-user] Clipping WMS Layer for Export to Geo PDF

[David Strip]

  
  
On 7/30/2021 1:37 PM, Stewart Holt
  wrote:

I
  am working on a GeoPDF map to use in the Avenza map app.
A couple of warnings about GeoPDFs and Avenza:
1. Even if you upload your maps as GeoPDFs, Avenza will rasterize
the map on upload. 
2. At least as of about six months ago, Avenza's rasterizer did not
correctly rasterize line pattern fills. The color was changed and
the fill was a solid fill, not a line pattern. Avenza was aware of
the problem, but didn't have a fix at the time. 

  

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Re: [Qgis-user] GPS Points CRS and delete doubles

[David Strip]

  
  
On 7/8/2021 6:53 AM, L.W. wrote:

But the
  more important question for me is how to delete double points
  
  not only by coordinate but with use of the timestamp in the same
  table.


Take a look at GPSBabel - it has a large number of tools for
managing GPS tracks
  

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Re: [Qgis-user] using georferenced PDF map files as layers

[David Strip]

  
  
On 7/7/2021 3:47 PM, robertd...@tpg.com.au wrote:

  
  
  
  
Hi,  I have the latest ver. of QGIS, I have
  imported two georeferenced PDF maps but need to delete the
  boarders and legends to stitch the two into one map while
  retaining the georef. Data for use in Avenza.  Cannot find in
  the excellent docs and tutorials. Can anyone advise please.
Keep up the good work folks.
 
Kind
regards,
Robert
M. Dare  OAM
robertd...@tpg.com.au 
Mob. 0428503385
 

  

Some georeferenced PDFs (for example, from QGIS) are vector
representations that maintain the layer structure. If that's the
case, you likely can turn off the borders and legend. Many more,
however, are just a wrapper around a raster image, in which case all
you can do is clip the layer to remove the elements you don't want.


You mention that your target is Avenza. I will point out that by the
time a user downloads your map from the Avenza store, it has been
rasterized, so you may as well rasterize it in QGIS and just upload
a geotiff. In addition, I've had problems with Avenza's handling of
pattern fills as simple as diagonal hashes, so I ended up exporting
as a geotiff for that reason. And finally, QGIS geo-pdfs can't
represent transparency in layers styles, so that too will push you
towards a tiff export.


  

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Re: [Qgis-user] replace '\' problem

[David Strip]

  
  
On 6/29/2021 5:28 PM, Marcos wrote:

  
  I was trying to replace the '\' using the replace () function, but it didn´t work
anyway.
It's
  probably a standard/default problem or a 'reserved (not a)
  word'.


  

Just a guess, but \ is commonly used to indicate special characters.
eg, \n = newline.
Try using \\
  

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Re: [Qgis-user] Shifting polygon boundaries

[David Strip]

  
  
On 6/18/2021 4:44 PM, Charles
  Dixon-Paver wrote:

If
  you have already digitized the new boundary as a line feature you
  can use processing tools to split the boundary areas with the line
  features, but you will still have to merge in an edit session with
  the digitizing tools.

I think you could just dissolve the two polygons without resorting
to an edit session.


  

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Re: [Qgis-user] Snapping adjoining existing polygons

[David Strip]

  
  
On 6/12/2021 4:20 PM, Pat Brown wrote:

I
  have 2 shape files. One, which has been accurately digitised,
  contains provinces. The second one, which has been badly
  digitised, contains regions within the provinces. I now need to
  edit the regions so that their boundaries snap to the boundaries
  of the provinces where they are adjacent. I think something like
  snap and trace should work but I cannot figure out how to do this.
  Can anyone please advise? 

If I understand your task, a quick way to do the job would be move
the region vertices that are close to the province boundary so they
all lie outside the province. Now clip the region to with the
province boundary.
I think you will need to do this province-by-province, but that
still is probably easier than snap and trace.

Badly digitised region 

Shifted vertices  


clipped feature  

  

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[Qgis-user] Saving *raster* layer style to geopkg?

[David Strip]

  
  
Is it possible to save a r*aster* layer style to a geopackage? I
know how to do it for a vector layer, but can't find it for a
raster.
I'm using 3.16.7 LTR


  

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Re: [Qgis-user] Field calculator - converting string to int with possible NULL values

[David Strip]

  
  
To answer my own question - 
My problem occurred in a layer that was joined to a csv file. I had
"NULL" values where there was no matching join field, as one might
expect.
But it turns out that the csv file had the string "null" in an
otherwise integer column for missing entries. Thus, when I thought
the field calculator was rejecting NULL values, it was actually
rejecting the "null" string.

Sorry for the distraction.
    
    On 5/14/2021 4:21 PM, David Strip wrote:

  
  I have a string field I wish to convert to int. A small subset of
  the records contain NULL.
  I tried the following in the field calculator:
  
  case
when ("bb_usage" IS NULL) then 0
else to_int("bb_usage"")
end
  
  When I look at the preview, the result is correct whether or not
  the field contains int or NULL. But when I try to run it, I get an
  error:
   
          
  
  I also tried
  
  case
when ("bb_usage" IS NULL) then 0
when  ("bb_usage" IS NULL) then to_int("bb_usage")
end
  
  and get the same error.
  
  I tried
  if ("bb_usage" IS NULL, 0, to_int("bb_usage"))
  
  same error.
  
  I know there are workarounds, but why don't any of these work? Why
  does to_int get evaluated on the NULLs?
  
  
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[Qgis-user] Field calculator - converting string to int with possible NULL values

[David Strip]

  
  
I have a string field I wish to convert to int. A small subset of
the records contain NULL.
I tried the following in the field calculator:

case
  when ("bb_usage" IS NULL) then 0
  else to_int("bb_usage"")
  end

When I look at the preview, the result is correct whether or not the
field contains int or NULL. But when I try to run it, I get an
error:
 
        

I also tried

case
  when ("bb_usage" IS NULL) then 0
  when  ("bb_usage" IS NULL) then to_int("bb_usage")
  end

and get the same error.

I tried
if ("bb_usage" IS NULL, 0, to_int("bb_usage"))

same error.

I know there are workarounds, but why don't any of these work? Why
does to_int get evaluated on the NULLs?
  

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Re: [Qgis-user] (no subject) (elevation question)

[David Strip]

  
  
In the course of trying to find what
  geoid model Garmin uses, I found this on a
Garmin support page:
  . It is not uncommon for satellite heights to be off
from map elevations by +/- 400 ft. Use these values with caution
when navigating.
  
  Apparently some, but not all, models of the Garmin64 have a
  barometric altimeter. Depending on your actual model, this may or
  may not apply.
  
  
  On 4/20/2021 8:23 PM, Nicolas Cadieux wrote:


  Hi,
  
  
  David gave you a very good answer. Your looking at a 11 meter
  difference.  That is not much.  The first thing would be to look
  at the gps measurement.  (Any trees? Good satellite constellation?
   Any obstacles?). At best, your looking at a 6 to 10 meter error
   vertically. SRTMs are affected by trees.  That would make the
  SRTM higher (not your case).  Last thing to look at the the
  differences between the gps geiod model (a model of the average
  sea level).  SRTM use EGM96.  Your GPS probably uses something a
  bit more modern. You can easily get a 5 meter error between two
  Geiods.

  

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Re: [Qgis-user] (no subject) (elevation question)

[David Strip]

  
  
The 30m resolution of SRTM data refers to the spatial resolution,
not the resolution of the elevation reading. A number of factors
come into play when determining the vertical accuracy of SRTM data,
but according to this link,
the RMS error for SRTM vertical measurements is 3.56M. Because of
the configuration of the satellites used to calculate elevation with
a GPS, the vertical resolution is significantly worse than the
horizontal resolution. Further complicating matters, many Garmin
units contain a barometric altimeter which is preferred over the GPS
reading by the software. However, unless you calibrated the sensor
at a known elevation before starting your readings, you have no idea
how accurate it is. 
TL:DR - the SRTM value is probably better than your GPS reading.

On 4/20/2021 5:45 PM, jean Lukusa wrote:

  
  Hi all .
I hope you are doing fine.
I have experienced an issue:
The elevation taken in the field with gps
  garmin64 is 623 m but the one given by SRTM download from Qgis
  is 612m.
How can I interprete this gap knowing that SRTM
  resolution is 30 meters.
  
  Jean Lukusa

  



  

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Re: [Qgis-user] Extract Layers from an online web map

[David Strip]

  
  
Andrea Giudiceandrea wrote
> https://leafletjs.com/examples/choropleth/us-states.js

> Just download it, edit the file with a text editor and remove the string
> "var statesData = " at the beginning and the semi colon ";" at the end, and
> then you will be able to import and visualise it in QGIS.

I believe the geojson spec also requires an newline after the closing bracket. The .js just reaches EOF which is an error, at least in the on-line validator.
In simpler words - your file must end with a blank line. 
 

  

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Re: [Qgis-user] Extract Layers from an online web map

[David Strip]

  
  
On 4/17/2021 12:41 AM, Andrea
  Giudiceandrea wrote:


  David Stri wrote

  
you can examine the source code for the page and find the
geojson files and download them to your disk and then convert them
to shapefiles.

  
  Hi,
it seems examining the source code of the page is not needed.

The geojson data file is directly available on the page, linked in the "Data
Source" section as us-states.js
https://leafletjs.com/examples/choropleth/us-states.js

Regards.

Andrea


That's true in this specific case in which the map is part of a
tutorial. I was assuming the question was about the more general
case.
  

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Re: [Qgis-user] Extract Layers from an online web map

[David Strip]

  
  
On 4/16/2021 4:42 PM, krishna Ayyala
  wrote:


  Hello,
  I am reposting this question.
  
  
  Is it possible to export this map as a shape file? 
  
  Regards.
  
  
  

The layers in the leaflet map you linked to are represented by
geojson files. These files are downloaded to your browser, so in
principle you can examine the source code for the page and find the
geojson files and download them to your disk and then convert them
to shapefiles. You would still need to recreate the styling.
  

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Re: [Qgis-user] background data

[David Strip]

  
  
In addition to using a basemap solution as proposed in the previous
answers, you could download vector data for boundaries and cities
from Natural Earth, among
other sources.
This would allow you to style the background information as you
desire. 


  
On 15.04.21 20:23, Cassia Pahim wrote:

  


  

  Hello! I am searching for data of a background map where I can show my layers on the east coast of Canada and US. I would like a background with the names of the cities and not a satellite image. Do you guys know where I could find that kind of data? Thanks a lot!!

Cassia



  


  

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Re: [Qgis-user] Generate the bearing in the attribute table

[David Strip]

  
  
On 4/8/2021 6:32 PM, chris hermansen
  wrote:

Please
  correct me if I am wrong but are not the start and end points of a
  polygon the same?
I believe he's referring to the start and end point of each edge.
  

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Re: [Qgis-user] Generate the bearing in the attribute table

[David Strip]

  
  
are you asking for the bearing between each successive pair of
vertices? ie, the bearing from vertex n to vertex n+1?
  

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Re: [Qgis-user] Compressing rasters in geopackage?

[David Strip]

  
  
On 4/7/2021 7:59 PM, Nicolas Cadieux
  wrote:

Hi,
  This is from an earlier email exchange. It may help.  Look
for « Geopackage file data loss issue » in the mailing list.


Thanks for the pointer and the information. I had done some more
reading and was a bit confused by the reference to tiles, but that's
apparently how rasters are stored. 
The gdal references explain the default settings, which are
compressed, just not at the highest level. 
The warning about the lossy compression as default is very useful,
thank you.


  

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[Qgis-user] Compressing rasters in geopackage?

[David Strip]

  
  
Are raster layers saved to geopackage compressed? I have a
geopackage with two raster layers in it and they appear to be
uncompressed. Both layers are about 11K x 14. One is byte, the other
is float32 and the geopackage is around 500M, consistent with no
compression. 
I tried doing an "export" of the layer to a geopackage (as opposed
to dragging it into the geopackage in the file browser pane), but
the only available profile under Create Options is "default". Do I
need to type compression options explicitly?

Thanks
David
  

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Re: [Qgis-user] Fill-down with QGIS expressions

[David Strip]

  
  
On 3/28/2021 2:05 PM, Alexandre Neto wrote:

  
  Sorry,


Can you be more clear? It's not clear to me what
  you are trying to accomplish.



  

Here's some sample data he posted on Github:




  data
  nuts2
  zona
  zona_fill


  2020-11-09T17:00:00
  ITF1
  
  
  
  


  2020-11-10T17:00:00
  ITF1
  arancione
  arancione


  2020-11-11T17:00:00
  ITF1
  
  
  arancione


  2020-11-12T17:00:00
  ITF1
  
  
  arancione


  2020-11-20T17:00:00
  ITF1
  
  
  arancione


  2020-11-21T17:00:00
  ITF1
  
  
  arancione


  2020-11-22T17:00:00
  ITF1
  rossa
  rossa


  2020-11-23T17:00:00
  ITF1
  
  
  rossa


  2020-11-24T17:00:00
  ITF1
  
  
  rossa


  2020-12-04T17:00:00
  ITF1
  
  
  rossa


  2020-11-09T17:00:00
  ITF5
  
  
  rossa

  


the column labeled "zona" has entries followed by some number of
blank entries.
I believe he wants to create a column "zona_fill" that contains the
last non-blank entry in "zona" that's above or equal the current
row.


  

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Re: [Qgis-user] Building 3D from SRTM or DEM

[David Strip]

  
  
On 3/26/2021 1:40 PM, jean Lukusa
  wrote:

Hi
  all ,
  Can you help how to build 3D from 2D data
including SRTM or DEM


Not sure exactly what you're trying to achieve, but the qgis2threejs
plugin might be what you want. 
  

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Re: [Qgis-user] How to filter expression in aggregate

[David Strip]

  
  
On 3/14/2021 5:28 PM, Andrea Giudiceandrea wrote:

  David Strip-4 wrote

  
aggregate( 'B','sum', "Confirmed", "Country_Region" 
ILIKE attribute($currentfeature, 'SOVEREIGNT')) 

  
  
Hi David,
in the filter the source feature can be accessed with the variable @parent
https://docs.qgis.org/3.16/en/docs/user_manual/working_with_vector/functions_list.html#aggregate

aggregate( 'B','sum', "Confirmed", "Country_Region" ILIKE attribute(@parent,
'SOVEREIGNT'))




that did it. Does that mean that attribute(@parent, ...) is
the value of the attribute for the feature for which the attribute
is being calculated?
And what does $currentfeature mean? Is it evaluated to the current
feature of Layer B, not A?
  

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[Qgis-user] How to filter expression in aggregate

[David Strip]

  
  
Let's say I have two layers with the following attributes:
Layer A - SOVEREIGNT, Field2, Field3, ...
Layer B - Country_Region, Confirmed, ...

I want to aggregate the Confirmed field of Layer B into Layer A. 
I try to create a virtual field in Layer A with the _expression_
 aggregate( 'B','sum', "Confirmed", "Country_Region"  ILIKE 
attribute($currentfeature, 'SOVEREIGNT'))
but the value is always zero. 

What am I not understanding?
Thanks

David



  

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[Qgis-user] Nodata pixels in the raster calculator

[David Strip]

  
  
It appears to me that the raster calculator treats a nodata pixel
the same as any other pixel, performing the requested operation on
the nodata pixel as if it were a valid value. In addition, it
appears that there is no way to create an output raster that has a
nodata value.*  Are these two statements correct?

I know that I can write a formula
        (raster@1 = ) *  + (raster@1 !=
) * 

but this requires you know the nodata value. Even in this case, the
resulting raster does not encode that value as nodata.







*The GDAL processing algorithm "Raster Calculator" does allow
specifying a nodata value
  

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Re: [Qgis-user] Problem running GRASS r.lake from Qgis

[David Strip]

  
  
I ran the same data in QGIS 3.10.5 and it ran without problems. 


On 2/24/2021 3:51 PM, David Strip wrote:

  
  Qgis 3.16.2, GRASS 7.8.4, Win 10.
  
  I'm attempting to run the r.lake processing algorithm. If I select
  "Temporary layer" for output, or specify a new file, I get and
  error - "grass r.lake The following layers were not correctly
  generated.". I believe this is because the script always specifies
  --overwrite,
  which apparently fails if the file doesn't
  already exist. 
  I then try to run specifying a file that already exists. This
  file is a copy of the input DEM layer used to run the
  algorithm ,so it has the same properties as the input layer.
  The algorithm runs to completion and adds the new layer to the
  map, but it is appears to be the same  as the file that was
  supposed to be overwritten.
  
  My input layer can be found here.
  I load the file into a empty project. CRS is 4269
  I select r.lake
  Select the only layer as the Elevation input
  Set Water level =2500
  Select a seed - The value of the DEM surface at
  the seed point is around 2000.
  Select
  an existing file for output
  Accept all other defaults, run algorithm.
  
  The dump of the script parameters is:

  


{ '-n' : False, 'GRASS_RASTER_FORMAT_META' : '', 'GRASS_RASTER_FORMAT_OPT' : '', 'GRASS_REGION_CELLSIZE_PARAMETER' : 0, 'GRASS_REGION_PARAMETER' : None, 'coordinates' : '-106.503588,36.309857 [EPSG:4269]', 'elevation' : 'C:/Users/David/Documents/Geodata/Topo maps/Abiquiu/USGS_13_n37w107.tif', 'lake' : 'C:/Users/David/Documents/Geodata/geoTemp/lake2.tif', 'seed' : None, 'water_level' : 2500 }


  
  I've run this with the original input file in EPSG:4269, and against the same file converted to UTM13N - EPSG: 26913 - same results in either case.
  

  What am I misunderstanding about how to run this?
Thx.
  

  David
  

  

   
  
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[Qgis-user] Problem running GRASS r.lake from Qgis

[David Strip]

  
  
Qgis 3.16.2, GRASS 7.8.4, Win 10.

I'm attempting to run the r.lake processing algorithm. If I select
"Temporary layer" for output, or specify a new file, I get and error
- "grass r.lake The following layers were not correctly generated.".
I believe this is because the script always specifies --overwrite, which
apparently fails if the file doesn't already exist. 
I then try to run specifying a file that already exists. This
file is a copy of the input DEM layer used to run the algorithm
,so it has the same properties as the input layer. The algorithm
runs to completion and adds the new layer to the map, but it is
appears to be the same  as the file that was supposed to be
overwritten.

My input layer can be found here.
I load the file into a empty project. CRS is 4269
I select r.lake
Select the only layer as the Elevation input
Set Water level =2500
Select a seed - The value of the DEM surface at
the seed point is around 2000.
Select
an existing file for output
Accept all other defaults, run algorithm.

The dump of the script parameters is:
  

  

  { '-n' : False, 'GRASS_RASTER_FORMAT_META' : '', 'GRASS_RASTER_FORMAT_OPT' : '', 'GRASS_REGION_CELLSIZE_PARAMETER' : 0, 'GRASS_REGION_PARAMETER' : None, 'coordinates' : '-106.503588,36.309857 [EPSG:4269]', 'elevation' : 'C:/Users/David/Documents/Geodata/Topo maps/Abiquiu/USGS_13_n37w107.tif', 'lake' : 'C:/Users/David/Documents/Geodata/geoTemp/lake2.tif', 'seed' : None, 'water_level' : 2500 }
  


I've run this with the original input file in EPSG:4269, and against the same file converted to UTM13N - EPSG: 26913 - same results in either case.


What am I misunderstanding about how to run this?
Thx.


David



  

  

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Re: [Qgis-user] How to limit number of "Recent Projects" listed - Correction

[David Strip]

  
  
If you just want to hide the recent projects on the opening screen,
go to Settings->General->Project Files and select something
other than "Most Recent" "Welcome Page".



If you still want a list of recent projects, but a shorter list, go
to Settings->Advanced and search for maxRecent and change the
value. This will also change the length of the list of recent
projects in Project->Open Recent

  

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Re: [Qgis-user] How to limit number of "Recent Projects" listed

[David Strip]

  
  
If you just want to hide the recent projects on the opening screen,
go to Settings->General->Project Files and select something
other than "Most Recent".



If you still want a list of recent projects, but a shorter list, go
to Settings->Advanced and search for maxRecent and change the
value. This will also change the length of the list of recent
projects in Project->Open Recent

  

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Re: [Qgis-user] Lat Lon Tools question

[David Strip]

  
  
On 2/6/2021 11:33 AM, chris hermansen wrote:

  
  
Your lat long 35,-106 are far west in the
  northern hemisphere. Therefore the UTM zone is 13N not 13S.


This is somewhere near Memphis Tennessee if I am
  not wrong.


  

Actually, that's pretty close to me. It's in Los Alamos, NM. (I'm
about 75 miles WNW).

There is some confusion about the naming of UTM zones. According to
Wikipedia,
the latitude bands are not part of the UTM description, but rather
from the MGRS. Nonetheless, UTM grid references are sometimes given,
creating the ambiguity between 13S meaning latitude band S vs.
meaning a UTM coordinate south of the equator. In the case of the
coordinates given here, 13N means zone 13 north, and is not a
latitude band reference. 

  

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Re: [Qgis-user] [QGIS-Developer] New QGIS Date/Time Tools Plugin

[David Strip]

  
  
On 1/28/2021 11:10 AM, C Hamilton
  wrote:

In
  thinking about it, if the data set is too large to include with
  QGIS, it might be worth having a simplified geometry data set
  included and if the user wants more precise data then they can
  download it and use it instead.
I was wondering this same question when this arrived in my mailbox.
It seems to me that one could achieve a very substantial reduction
in size (>90%?) while creating only a very small increase in the
error rate, as it seems these will only occur in areas where
boundaries contain very small scale details. I'll admit that have
not attempted an empirical test of this conjecture. 

  

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Re: [Qgis-user] How do I achieve this symbol effect?

[David Strip]

  
  
On 1/24/2021 9:34 AM, Charles
  Dixon-Paver wrote:

I
  can think of 2 easy ways to do this (if I understand the
  requirements correctly), using either rule based rendering, or the
  geometry generator on with stacked symbols. I imagine rule based
  rendering might be more performant in some situations depending on
  the queries used, but for our use case I feel either would be
  appropriate.
  
  


Your example was right on the mark. I either forgot or never knew
that a single polygon can be styled by multiple rules in the layer.
Thanks.

  

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[Qgis-user] How do I achieve this symbol effect?

[David Strip]

  
  
To highlight a specific polygon I'm using the drawing effects to
translate and drop shadow as the styling for a single polygon in the
layer by using categorized symbology.


So far, so good. But what I really want is this, where the place the
original polygon is cut from is filled in like the rest of the
layer.



I did this by duplicating the polygon and coloring it to match. My
question is whether this can be achieved without duplicating the
polygon.
If I add a "source" layer after the drop shadow the region is
filled, but in purple, because that's the color for that category.
Is there anything else to try to get the region filled in the
default color that doesn't involve creating a duplicate polygon?

  

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Re: [Qgis-user] saving all temporary layers?

[David Strip]

  
  
On 1/21/2021 10:13 PM, Michael Dufty
  wrote:


  Not
  exactly what you are asking for, so it may not suit, but I
  find the “memory layer saver” plugin invaluable.
  When
  using this memory layers are not lost when you close QGIS

Thanks for the pointer. I'll check whether this serves my needs.
  

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[Qgis-user] saving all temporary layers?

[David Strip]

  
  
Before I write my own, does anyone have a script to share
(processing or otherwise) that saves all temporary layers in a
project, preferably to a geopackage?
Thanks
David
  

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Re: [Qgis-user] How to use QgsProcessingLayerPostProcessorInterface?

[David Strip]

  
  
On 1/20/2021 5:25 PM, Etienne Trimaille
  wrote:


  Can you try that?
  
  
  
class Renamer(QgsProcessingLayerPostProcessorInterface):
instance = None

def postProcessLayer(self, layer, context, feedback):
layer.setName('DiffLayer')

@staticmethod
def create() -> 'Renamer':
Renamer.instance = Renamer()
return Renamer.instance



In your processAlgorithm method() :


context.layerToLoadOnCompletionDetails(
data[layer].id()
).setPostProcessor(
Renamer.create()
)



  

That works. Thanks. 
I made a small change because I didn't know  what data[layer] was
referring to. Instead I used
   
context.layerToLoadOnCompletionDetails(self.dest_id).setPostProcessor(Renamer.create())

where self.dest_id is the second value returned from the
ParameterAsSink call.

Your solution leads me to conjecture there is either a temporal
scoping issue with just using Renamer() in the call to
setPostProcessor(), or else it has something to do with how Python
passes parameters by object reference. Either way, by the time the
postProcessorLayer is called, there's nothing there. This leads to a
slightly different solution that is more flexible if there are
multiple output layers:
class Renamer
(QgsProcessingLayerPostProcessorInterface):
    def __init__(self, layer_name):
    self.name = layer_name
    super().__init__()
    
    def postProcessLayer(self, layer, context, feedback):
    layer.setName(self.name)
    
renamer = Renamer("DiffBuf")


  context.layerToLoadOnCompletionDetails(self.dest_id).setPostProcessor(renamer)

  

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