Re: [Qgis-user] 3.20.1 fails on Linux Mint

[j . huber]

Hi,

same problem here on Fedora 34 (no GUI, no error, qgis process at 100%
on one core), same fix.

Thanks!
Jochen

Am 21.07.21 um 22:29 schrieb Richard Greenwood:
> Same here -
> removing ~/.local/share/QGIS/QGIS3/profiles/default/symbology-style.db
> fixes the issue.
>
> Many thanks!
> Rich
>
> On Wed, Jul 21, 2021 at 11:47 AM Fernando M. Roxo da Motta
> mailto:pe...@roxo.org>> wrote:
>
> On Wed, 21 Jul 2021 13:05:14 -0400, Randal Hale
>  > wrote:
>
>
> > Removing the
> > ~/.local/share/QGIS/QGIS3/profiles/default/symbology-style.db worked
> > for me - it was recreated upon startup.
>
>   Just tried and it worked.
>
>   Sdls.
>
> >
> > Randy
> >
> >
> > On 7/21/21 12:56 PM, Andrea Giudiceandrea wrote:
> > > Il 21/07/2021 18:42, Andrea Giudiceandrea ha scritto:
> > > 
> > >> See https://github.com/qgis/QGIS/issues/44299
>  for some
> > >> workarounds: it seems the isse is related to the
> > >> "symbology-style.db" file in the profile folder. 
> > >
> > > The correct link to the Issue on GitHub is
> > > https://github.com/qgis/QGIS/issues/44293
> .
> > >
> > > Regards.
> > >
> > > Andrea
> > > ___
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> https://lists.osgeo.org/mailman/listinfo/qgis-user
>  
> >
>
>
>
>
>
>
>
>
>   Roxo
>
> -- 
>  Non luctari, ludare ---+ WYSIWYG
> Fernando M. Roxo da Motta  >              | Editor?
> Except where explicitly stated I speak on my own behalf.|  VI !!
>                 PU5RXO | PX5Q6048                       | I see text,
>  Quis custodiet ipsos custodes?-+ I get text!
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>
>
> -- 
> Richard W. Greenwood, PLS
> www.greenwoodmap.com 
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Re: [Qgis-user] Did scale change outputting to PDF?

[j . huber]

Hi John,

as I understand it, you created the base map in QGIS. If you use the
measure tool in QGIS to get the distance between two distinct features
in the map (e.g. road intersections) and then measure the same distance
on the printed base map with a ruler, it should be possible to calculate
the scale. Maybe use two distances, one aligned more or less
horizontally and one vertically, to check if the scaling is proportional.

As Andreas pointed out, it is probably a problem with the settings when
the PDF was printed. In my experience it is a good idea to go to print
shops usually working for architects and engineers since they are
familiar with the importance of scaling (for advertising etc. it is more
important that the whole content is printed, so that scaling might be
used to fit the output to the printable area without potential cropping).
You can print directly to a plotter in QGIS if you have access to the
device, avoiding the PDF detour.

EPSG 2264 should be fine. Units should be US feet.

Regards
Jochen


Am 27.05.21 um 07:15 schrieb John Antkowiak:
> Hi. This plan was too simple to fail - but it failed. The charity
> whose project this is needed a large (that is... massive) paper wall
> map on which to plot and rethink its delivery driver assignments. Both
> drivers and delivery addresses are subject to change from week to week
> but it's not a pizza delivery; this is a regular run to supply people
> in a bad way. So the plan was to print the base map (roads and road
> names and county boundaries only) and then print 8.5 x 11 address maps
> with parcel data and orthos. That way, the base maps don't change but
> the physical parcel layer is flexible. (On top of that is a third
> paper layer indicating which drivers go where so someone can stand
> back and take in the whole picture graphically. Not a cutting-edge
> state of the digital art solution, but not everyone is cut out for
> that. It is what it is.) In order for this to work, the parcel maps
> have to be the same scale as the base map. Which they were... in QGIS.
>
> We have to convert all the maps to PDF to print them, and we had to
> send the base map PDFs to FedEx/Kinkos to print the 9 map grid panels
> at 42" by 62" each. 
>
> When we got the big base maps up on the wall, we discovered the scale
> did not match the 8.5" x 11" parcel maps output to PDF and printed
> from home. It's not off by a lot, but it's enough to be painfully
> obvious from a single standard size sheet of paper. I don't know how
> to reverse engineer the big map scale precisely enough to enter a new
> scale number in the QGIS Print Layout. I didn't foresee it because
> this never would've been a conceivable scenario at the engineering
> firm where I picked up my meager GIS skills. (ArcMap sent a map
> directly to the plotter without interim steps.) There was no scale bar
> on the map. It shouldn't have been needed for this.
>
> Did something happen to the map scale when QGIS output the map to PDF?
> Could the size of the image on the pdf page have been adjusted
> manually or otherwise when being sent to a plotter with 42" paper?
> Could the image have been distorted horizontally differently from
> vertically? For the life of me, I cannot trial-and-error guess at a
> scale to enter. I've gone through dozens of new 8.5" x 11" test maps
> trying to guess the correct scale.
>
> Any ideas? 
>
> Thank you all -
>
> John A.
>
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Re: [Qgis-user] Georeferencing a DXF file

[j . huber]

Hi Walt,

I would load the dxf file with the modified building in QCAD and 
move/translate the data there. After saving the modified dxf file, this 
should import in QGIS at the correct location.


You will need two reference points from the existing building structure 
- you could for example export the existing data set from QGIS to dxf 
and load it in QCAD as a reference or write the coordinates of two 
points out manually in QGIS.


Regards
Jochen

Am 03.02.21 um 20:10 schrieb Walt Ludwick:
I've received a 3D AutoCAD file from an architect that i managed to 
convert into 2D .dxf format and import into my QGIS project, but it is 
out-of-scale and out-of-place, so i guess i need to add some 
georeferencing coordinates to the file.


This should be easy enough, since it's an accurate representation of a 
building that's already in the project -with an additional wing tacked 
on- so i'm thinking i could just use a few corners of that existing 
buildings as ground control points, and map them to the corresponding 
corners on this .dxf model, then maybe all other co-ordinates could be 
automatically generated by some tool, if i could just find the right 
one for the job.


Is there in fact any such easy way to do this thing?

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Re: [Qgis-user] wishing for accurate lattitude/longitude from, a cell phone

[j . huber]

Hi Maria,

the position of the base station at the entrance of the valley sounds
good. Before you invest a lot of money, you could rent a system and try
it out in the field. Most local dealers should have devices available
for rent or tests.

The problem with wet conditions could have to do with multipathing
effects. Probably a choke ring antenna will be better in these
conditions. You could try an experiment: Put your GPS in a flat box
which is covered with some conductive material (eg aluminium foil) so
that it only "sees" signals from above (the visible sky), not from below
or the lower sides. See if this changes the resulting accuracy.

Using a GPS antenna mounted on a pole has the advantage that your body
does not obstruct parts of the visible sky. When measuring near a steep
slope, be sure to stand on the side of the slope where the GPS can't
"see" the sky anyway. I know surveyors who use very long poles (like
3-4m) to position the antenna above the lower layer of vegetation. You
get errors due to the lack of verticality but much better reception.

You can't expect to get cm accuracy in the conditions you describe, at
least not with short-time measurements. For this you need phase tracking
which is very sensitive even to short obstructions of a satellite signal
(canopy).

Unfortunately it sound like you don't have sight contact on ground level
either, so a GPS base station as a reference and a total station for
measuring the individual points won't be an option.

Regards
Jochen



Am 28.05.20 um 01:53 schrieb Priv.-Doz. Dr. Maria Shinoto:
> Hi fellow archaeologists ;-), 
>
> there is so much precious information in this thread. 
>
> Now one question about precision and accuracy: As I said, we work in a 
> densely forested area, there is not just the canopy of the trees, but two to 
> three levels below with dense ground cover and bamboo walls. Still, we get 
> excellent (precise) results with consumer level handhelds and smartphones. 
> But the accuracy is not good under certain conditions: Water and muddy ground 
> seems to be an obstacle for GPS as well as the steep slopes. We get very 
> precise results in certain places, but they are in certain cases several 
> meters apart from the "real" place -- which we can test with the LiDAR DTM. 
> Dry underground and measurement about 10m apart from the slopes result in 
> accurate positions, but any measurement point closer to the slopes leads to a 
> consistent error in the measurement -- across devices. 
>
> I still wonder whether these conditions are suitable for any GPS technology 
> or whether working with a fixed station and a rover would be OK. I could then 
> think of positioning the station at the entrance of the valley and walking up 
> narrowing valley with the rover.
>
> Best, 
> Maria
>
>
>> Am 28.05.2020 um 02:17 schrieb Nicolas Cadieux 
>> :
>>
>> Hi Garth,
>>
>> I am also an archaeologist.  We use a single Sxblue 2 from GENEQ.  The unit 
>> was upgraded by the company so it’s takes in the Russian constellation now.  
>> The unit is very precise. When we go out on the field, we let le unit run 
>> one a Bench mark for a few hours.  We then process that position  In PPP or 
>> using nrcan gps tower if we are close to one.  The company give a really 
>> good service helping with both software support and hardware.  As everything 
>> in made and designed in Québec, they can take the unit appart and change 
>> individual parts and chips.  We did that one as the Bluetooth chip was now 
>> longer capable of working with Windows 10 (more likely the other way 
>> around). It had been Made for Windows 95.  For a few extra bucks, they 
>> changed the gps chip also.  The unit is basically a brick (Square and heavy) 
>> that connects to an external device like a laptop or a tablet.  No screens 
>> or anywhere fancy.
>>
>> https://geneq.com/land-surveying-geomatics/fr/fabricant/sxblue
>>
>> Nicolas Cadieux
>> Ça va bien aller!
>>
>>> Le 27 mai 2020 à 11:19, QGIS.USER  a écrit :
>>>
>>> Hi Garth,
>>>Thank you for the correction and the additional information. Much 
>>> appreciated.
>>>
>>> My current thinking is that in the archaeology we do, the intra-site 
>>> (relative) measurements are quite good but what is inaccurate is the 
>>> absolute measurements. We can set out our grids with cm accuracy but can 
>>> only locate them on the ground with 10s of metre accuracy. It would be good 
>>> to have a low cost way of establishing the absolute position even if that 
>>> took time and/or was off-line.
>>>
>>> Ray Carpenter,
>>> Chapel Archaeology
>>>
>>> -Original Message-
>>> From: Garth Fletcher [mailto:ga...@jacqcad.com] 
>>> Sent: 27 May 2020 15:25
>>> To: QGIS.USER; qgis-user@lists.osgeo.org
>>> Subject: Re: [Qgis-user] wishing for accurate lattitude/longitude from, a 
>>> cell phone
>>>
>>> Hi Ray,
>>>
>>> Apologies for the typo - I had typed iGS3, but iG3s is the right number.
>>>
>>> iGage 
>>> 

Re: [Qgis-user] wishing for accurate lattitude/longitude from a cell phone

[j . huber]

Hi,

while I agree that there are lots of bad examples of proprietary
formats, I want to say a few words to some of your examples:
It is true that OpenStreetMap data is difficult to handle -  this is not
because it is closed, but because it is open. When the project was
started the goal was to make it as easy as possible for people to
contribute to the dataset. Thus there are few restrictions which makes
it difficult to render or process the data. But the alternative would
probably have been to discuss the data format for years instead of
building an amazing open dataset...

While Garmin makes it difficult to upload custom maps to their units as
Nicolas wrote, many of their devices can be accessed as a USB drive and
waypoint/track data can simply be copied as .GPX-files. I have seen many
devices needing special software to transfer data, so this is actually easy.

When Google Earth first came to be, it was amazing - access to satellite
or aerial imagery had been expensive and difficult before. So I don't
have a problem with the fact that Google didn't make the data available
for everyone to use (probably license restrictions prohibit this).

Text files aren't often that simple - there are different encodings for
example which aren't advertised in the files, so you often have to guess
to get special characters right. They have no inbuilt validity checks,
so errors can not be easily recognised. In most use cases, structured
(XML) formats are preferable. And especially for large datasets, you get
much better performance and functionality using other formats like
Geopackage. The point in my opinion is that a format is open and well
documented.

Of course it is great if geodata is available to the public. In the EU,
there has been a lot of movement in the last years with more and more
data becoming available under open licenses, let's hope this continues.

Regards,
Jochen

Am 25.05.20 um 20:55 schrieb Falk Huettmann:
> Dear Chris et al,
>
> ...by using certain specific/clumsy formats -poorly documented ones -
> you can virtually exclude
> people from data and from Remote Sensing data and GPS etc.
> Google Earth as a  classic example, and GARMIN as another, or ESRI
> files, certainly NetCDF or many R packages even.
>
> In reality, you will see that all what is shiny and new - in demand-
> is to be sold, and usually not well publically shared.
> It takes many steps to get around it, if even that.
>
> While I have used OpenStreet maps, it was very clumsy; more bad
> examples exist, e.g. lack of metadata.
> Whatever companies tell ya, they want to sell more stuff (sell PR, or
> might face bankruptcy otherwise).
>
> And it is my hope that with QGIS we get to open access and open source,
> of these data, and any other.
>
> My format of choice is plain and simple ASCII text files for those
> reasons, perhaps using the 
> Virtual Machine as a platform forever (well, as long as that is
> reasonable, but not commercially driven).
>
> Keep me posted please; very best & thanks
>      Falk Huettmann
>
>
> On Mon, May 25, 2020 at 10:19 AM chris hermansen
> mailto:clherman...@gmail.com>> wrote:
>
> Falk and list;
>
> On Mon, May 25, 2020 at 10:48 AM Falk Huettmann
> mailto:fhuettm...@alaska.edu>> wrote:
>
> Dear List,
> I think these GPS high resolution suggestions are great; 
> thanks.
>
> But my real interest/question here is, how can we bring it
> home to QGIS ?
>
> I see GARMIN essentially trying to sell and impose on us their
> GIS system,
> same applies to OpenStreet Maps etc etc. So they try to
> privatize geography and public space and information, 
> which I am mostly opposed to.
>
>
> How is OpenStreetMap (I assume when you say "OpenStreet Maps" you
> mean "OpenStreetMap") trying "to privatize geography and public
> space and information"?   Not trying to start an argument here;
> this just seems completely contrary to what I know of
> OpenStreetMap, whose data is licensed under
> https://opendatacommons.org/licenses/odbl/1.0/
>
>
> Instead, I wonder how we can use QGIS and release the commercial
> data into Open Source and public use ?
> That's for HIGH RESOLUTION data discussed here.
>
> Thanks for such questions and solutions.
>
>
> [stuff deleted]
>
>
> -- 
> Chris Hermansen · clhermansen "at" gmail "dot" com
>
> C'est ma façon de parler.
>
>
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Re: [Qgis-user] Maximum value - attribute table

[j . huber]

Hi,

if the data is likely to change frequently, you might want to add a
virtual field. Thus, the MAX_AREA would always be up to date.

https://docs.qgis.org/3.10/en/docs/user_manual/working_with_vector/attribute_table.html?#creating-a-virtual-field

Regards
Jochen

Am 20.05.20 um 00:09 schrieb Riccardo D'Alvito:
> Hi!
> I would like to have information about a problem that I have.
>
> In the attribute table I have three columns: COUNT which indicates the
> name of the selected polygon, AREA_1 and AREA_2 which are two
> different area values.
> I would like to create a column called MAX_AREA that gives me the
> maximum value between the two AREA_1 and AREA_2 values relating to the
> same polygon.
>
> Thank you,
>
> Regars
>
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Re: [Qgis-user] wishing for accurate lattitude/longitude from a cell phone

[j . huber]

Hi Nicolas,

there are several potentially accurate GNSS modules available, even
sensitive choke ring antennas aren't that expensive. What's time
consuming and difficult is building a whole functioning system
(integration and software).
This would be a great university project - develop an open source GNSS
system based on relatively unexpensive components. It should be possible
to get the cost down from over a thousand to several hundred euro. This
could also be the basis for a "free" correction data service built on
private reference stations. Just dreaming...

I agree that for precision, "old school" technology is often better and
cheaper, although it requires more effort than simply pushing a button.

Regards
Jochen

Am 23.05.20 um 20:21 schrieb Nicolas Cadieux:
> Hi,
>
> I looked at the page.It looks like a neat project!  Buy time you buy a
> case, antenna... (I don’t think they come with on), your back into the
> price range of a forestry grade survey GPS unit.  I think the Emild
> single band gps (https://emlid.com/reachrs/ 
> ) is probably a better choice unless you
> really want to make this a learning project. But if I understand you
> are really on a shoe string budget.
>
> None of these Gps, by the way, would beat and old theodolite...  if
> you can establish or find a good gps position (look for the city or
> state geomatics services) or survey point,  a théodolite would give
> you survey grade positions.  City have these points on every few
> blocks.  You may be able to find A theodolite for free.  A second hand
> TotalStation could be better but that will be more difficult to find
> in those price ranges (Shoe string).  You can also rent equipment or
> find a college that would take this up as a teaching opportunity.
>
> Have fun!
>
> Nicolas Cadieux
> Ça va bien aller!
>
>> Le 23 mai 2020 à 13:52, Bernd Vogelgesang 
>> a écrit :
>>
>> 
>>
>> Unfortunately, the Forest Service Website went offline (maybe this
>> thread caused so much traffic that it broke down? ;) )
>>
>> I'm also desperately searching for an affordable way to have at least
>> some decent accuracy. I do not need submeter, but it would be
>> fantastic if it was possible to achieve meter accuracy.
>> I gave up on that Garmin stuff. They might be accurate, but I have no
>> chance to control this until I return home and put the recorded data
>> on screen over an aerial image. Those screens are a joke, and the
>> business logic that prevents me to put reasonable aerial imagery on
>> the device without paying a fortune is apita. Maybe this improved
>> cause I last checked 5 years ago.
>>
>> Mobile phones at least in my case seem to get worse. My Motorola from
>> 2016 had an accuracy of less than 4 meters, most of the time less than 2.
>> Now I bought a Huawei 30 pro cause of the camera (my first phone with
>> nice pictures!), but the accuracy is a nightmare. The position is
>> jumping around like a dog on rabies.
>> I also bought a bluetooth device (Navilock BT-821G) two years ago.
>> This is much better than the phones GPS, tho it only receives 20
>> satellites maximum (The phone claims to receive some 40). But also
>> this device sometimes, when walking a transect, is constantly 5
>> meters off the track for several several minutes.
>>
>> As apps averaging the positions were mentioned: Does anyone have a
>> recommendation on such apps (for Android)? I found some, but the
>> usability was not that great, and some even didn't enhance anything.
>>
>> Furthermore, I stumble upon an article about a module with u-blox
>> chip. https://www.sparkfun.com/products/16481
>> Does anyone have any experience with modules like this and what else
>> is needed? The description of all the stuff leaves me a bit puzzled.
>>
>> Cheers,
>>
>> Bernd
>>
>> On 23.05.20 18:17, Michael.Dodd wrote:
>>> https://besjournals.onlinelibrary.wiley.com/doi/full/10./j.2041-210X.2011.00118.x
>>> I did this quite a few years ago but in the graph in supplimentary
>>> material it shows how the accuracy of one consumer grade gps varies
>>> over time (at a fixed point). At the time I also did a lot more
>>> measurements using mobile phones and consumer grade units on a grid
>>> of points in the field, that was not published but basically the
>>> phones were often as good as if not better than the consumer grade
>>> gps units especially when using certain apps to average points.
>>> 
>>> 
>>> Where are my quadrats? Positional accuracy in fieldwork - Dodd -
>>> 2011 - Methods in Ecology and Evolution - Wiley Online Library
>>> 
>>> Introduction. There has been much written about sampling design,
>>> spatial scale and the need for permanent plots in ecological
>>> long‐term monitoring, for example, the paper on spatial scaling in
>>> ecology has been cited over 1500 

Re: [Qgis-user] wishing for accurate lattitude/longitude from a cell phone

[j . huber]

Hi Steve,

I think there are two different aspects to your question:
1) Accuracy of GPS Devices
I agree with others that you can't expect a better accuracy than the 10
to 30 feet you observed with a smartphone or a simple handheld GPS. This
might improve by averaging, but this takes time. Survey grade GPS
devices are very expensive. It is possible to get good modules and
antennas as components, but building a complete GNSS system requires
time and skill. This would reduce cost, but only to several hundred
instead of several thousand dollars, so this is no option in your case.
Besides, you will still need a correction data service (usually costly)
or use two receivers (rover and base).
So you probably have to stick with your phone, which is more flexible
regarding the software than a handheld GPS.

2) Software
The accuracy of the recorded position should not depend on where you tap
the screen - a good app should allow to record the current GPS position.
I am using Locus Map (Asamm Software) for a while now, it works quite
well, although it does not allow position averaging. There is a free
version, you could try that first.

Regards,
Jochen

Am 22.05.20 um 20:54 schrieb Stephen Sacks:
>
> In order to make widely available some wise advice, I'm sending to
> this list a message I received from Neil B.  In addition to Neil's
> message below, I want to mention that Nicolas Cadieux also provided
> similar information, saying I'd have to pay around $1,000 for
> equipment that gives consistently accurate location coordinates.  And
> thanks, also to Falk Huettmann and Bernd Vogelgesang for their replies. 
>
>
> Message from Neil B:
>
> Hello Stephen.
> Glad that you're having success. I would like to start off by saying
> that it is best to always reply to the mailing list and not directly
> to the person who submitted the email. Mailing lists work really well
> in that there is a pool of people out there who may be able to offer
> advice or may have an alternate method to solve the problem that may
> turn out to be a better way. On the flip side by maintaining the email
> chain through the mailing list, the follow up emails that provide
> information are stored in the archives which benefits anyone searching
> the internet to have the complete trail of information.
>
> As far as your results they are acceptable for the device you're
> using. GPS in phones are never built to precision survey standards and
> there is no reason for them to be. If you're within 30ft of where the
> phone thinks you should be then you can easily navigate the rest of
> the way by visual sight. High end equipment to achieve sub-inch
> accuracy is probably in the range of thousands of dollars. One thing
> to keep in mind is there is a difference between the accuracy of a
> device and to what level of precision they display. While the app on
> the phone may display 8 decimal places of a lat/long coordinate and
> tell you if you have moved a foot, it doesn't help that the coordinate
> it is displaying is out +/- 30 feet. The accuracy of a device can also
> be affected by the environment where the device is being operated. In
> regards to cell phones, they use multiple sources to determine
> location such as GPS, cell phone towers, and wifi points to perform
> the triangulation. Lack of line of sight to satellites, signals from
> cell towers bouncing off of surrounding buildings, or someone's
> wireless router using inaccurate position information can all affect
> the accuracy of what is being displayed on your phone.
>
> So the question is how are you determining that the coordinates are
> wrong? If you have information that you trust to be authoritative then
> adjust your points to those values and carry on. I have no advice or
> opinions on inexpensive devices that may help with a more accurate
> reading.
>
> Please do not respond directly to me. This email account is not
> actively monitored and I don't always have the time to follow up with
> the emails. All the best with your endeavours.
>
> ~Neil B.
>
> On Fri, May 15, 2020 at 7:52 PM Stephen Sacks  > wrote:
>
> Hi Neil,
>
>    With your help, I have successfully brought the corners of our
> gardens back from Pennsylvania to the Promenade here in Brooklyn
> Heights, New York.  Thank you.
>    At the risk of wearing out my welcome, I'm now asking for more
> advice.  My point features are approximately where they should be
> but not exactly, some points are just a few feet off and some are
> 10 or even 30 feet off.  I imported the data trying both EPSG 4326
> and 4269.
>    I'm now convinced that the problem is due to (1) my Google
> Pixel 3 cellphone, (2) the app I'm using ("Latitude Longitude"
> published by gps-coordinates), and  especially (3) my
> less-than-steady hands.  I capture coordinates by standing at
> spot, waiting for the blue dot to settle, and then touching the
> blue dot.  Often I