[Qgis-user] Topological editing now working when the data CRS is different from project CRS

[Sabin Kolarov]

Dear List,

 

does anyone have some observation how long does it take for a reported bug to 
be fixed?

I reported a serious regression in April, but it’s not fixed yet.

Here is the link:

https://issues.qgis.org/issues/21833#change-103941

 

Regards,

Sabin

 

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Re: [Qgis-user] [QGIS-Developer] Geodesic Line Simplification

[Nyall Dawson]

On Wed, 2 Oct 2019 at 01:30, C Hamilton  wrote:
>
> I am guessing this is working on Cartesian coordinates and not geodesic which 
> is fine if you have a local projection. I think I will go ahead and implement 
> some similar geodesic algorithms. Thank you for the GRASS link. It will help.

Hi Calvin,

I think there's a strong use case for adding this to the c++ API.
Would you be willing to put together a proof of concept in Python code
and I'll port it to c++ for you?

Nyall


>
> Thanks,
>
> Calvin
>
> On Tue, Oct 1, 2019 at 7:45 AM Áron Gergely  wrote:
>>
>> Hi Calvin and list,
>>
>> Have you looked at the GRASS GIS v.generalize tool? 
>> https://grass.osgeo.org/grass64/manuals/v.generalize.html
>>
>> The Douglas-Peucker algorithm is implemented there and I have used that with 
>> (topologic)success recently on many touching polygons. Should work for 
>> polylines too!
>>
>> Best regards,
>> Aron
>>
>> On 01/10/2019 08:19, Tim Sutton wrote:
>>
>> Hi
>>
>> On 26 Sep 2019, at 17:13, C Hamilton  wrote:
>>
>> Are there any geodesic QGIS algorithms that simplify lines? "Simplify" just 
>> uses the projection units of measure. If there isn't I thought I would add 
>> this to the Shape Tools plugin. I could easily implement the Douglas-Peucker 
>> algorithm using geodesic math.
>>
>> For GPS tracks I also see a need to throw out all points that are less than 
>> a certain distance or less than a certain time interval. I don't see any 
>> simplification algorithms that make use of time. Am I just missing them?
>>
>>
>> No I don’t think we have any time based simplifiers - would be a great 
>> addition!
>>
>> Regards
>>
>> Tim
>>
>>
>>
>>
>> Thanks,
>>
>> Calvin
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>>
>>
>>
>>
>>
>> Tim Sutton
>>
>> Co-founder: Kartoza
>> Ex Project chair: QGIS.org
>>
>> Visit http://kartoza.com to find out about open source:
>>
>> Desktop GIS programming services
>> Geospatial web development
>> GIS Training
>> Consulting Services
>>
>> Skype: timlinux
>> IRC: timlinux on #qgis at freenode.net
>>
>> I'd love to connect. Here's my calendar link to make finding time easy.
>>
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[Qgis-user] time in Attribute

[RMG]

Hello,

I am trying to figure out the duration between one day's survey begin time 
(e.g., 7:13:45) and end time (e.g., 9:39:53) in an attribute table of a line 
shape file. It has just two attributes begin and end. But $lengh returns an 
error message and cannot figure out the duration. I suspect that the fields are 
not in proper format. So, I try to update the fields with

to_time("begin")

Then, it says Eval Error: Cannot convert '7:13:45' to Time. 

What is a remedy? The “begin” and “end” are in string. 

Best wishes,

Reiko Matsuda Goodwin
Comoé Monkey Project
Guenon Conservation Community


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Re: [QGIS-it-user] Info PlugIn Form Value Relation

[Umberto Zulian]

Il mer 2 ott 2019, 21:53 Luca Bellani 
ha scritto:

> Salve, stavo oggi cercando una cosa per me, e mi pare che questa funzione
> sia
> giá presente nel core.
> Quando scegli VALUE RELATION come widget, in basso si apre il filtro, e
> nelle funzioni FORM trovi la current_value
>
>
>
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Re: [QGIS-it-user] Info PlugIn Form Value Relations, zz 22 s

[Umberto Zulian]

Il mer 2 ott 2019, 21:53 Luca Bellani 
ha scritto:

> Salve, stavo oggi cercando una cosa per me, e mi pare che questa funzione
> sia
> giá presente nel core.
> Quando scegli VALUE RELATION come widget, in basso si apre il filtro, e
> nelle funzioni FORM trovi la current_value
>
>
>
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Re: [QGIS-it-user] Info PlugIn Form Value Relation

[Luca Bellani]

Salve, stavo oggi cercando una cosa per me, e mi pare che questa funzione sia
giá presente nel core.
Quando scegli VALUE RELATION come widget, in basso si apre il filtro, e
nelle funzioni FORM trovi la current_value



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[QGIS-it-user] Filtri dinamici nella combobox della form

[Luca Bellani]

Salve, l'amico Salvatore Fiandaca ha un ottimo tutorial di come realizzare
filtri dinamici dei form, mettendo in relazioni diversi layer, usando un
plug di Alessandro Pasotti

https://www.youtube.com/watch?v=5wcEFLSLTCA

Mi chiedo: é possibile fare la stessa cosa, ma all'interno di 2 campi di uno
stesso layer?
Grazie!



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Re: [Qgis-user] Swamp identification

[Nicolas Cadieux]

Hi,

I see you have been pointed to the semi automatic classification plugin.  Note 
that Google Earth is not usable for such work unless you simply want to make a 
visual identification.  Landsat can be used.  You should look at various peer 
review papers if you want to make a good job.  This is not as simple as it 
looks.  Also, identifying the correct type of swamp, bog... is one of the most 
difficult things to do.

Nicolas

> Le 2 oct. 2019 à 08:19, jean Lukusa  a écrit :
> 
> Hi all .
> Would you  assist me how to identify swamp areas in a  landsat or googleearth 
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Re: [Qgis-user] Merge does work (at least not as I expect)

[Alexandre Neto]

The layer being multilinestring just mean that you can create features with
multi geometries in it. It says nothing about the actual features in it.

A quarta, 2/10/2019, 17:04,  escreveu:

> On 10/2/2019 9:41 AM, Alexandre Neto wrote:
>
> Hi,
>
> Using your layer directly into merge lines algorithm worked properly on
> QGIS 3.4 in Linux. That is, in the end, I got one single feature that is no
> longer multi. (if I try to go multipart to single part I can't get the
> individual segments).
>
>  When I merge on the layer, I get a new layer that still reports as
> multi-linestring
>
>
>
> However, it is internally different since now when I export as a gpx file,
> it is a single segment, which was the goal. Curious that it still reports
> the type as MultiLineString.
>
>
> Hope it helps,
>
> Indeed, it solves the problem
>
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Re: [Qgis-user] Merge does work (at least not as I expect)

[qgis-user]

  
  
On 10/2/2019 9:41 AM, Alexandre Neto
  wrote:


  Hi,
  
  
  
  Using your layer directly into merge lines algorithm worked
properly on QGIS 3.4 in Linux. That is, in the end, I got one
single feature that is no longer multi. (if I try to go
multipart to single part I can't get the individual segments).

 When I merge on the layer, I get a new layer that still reports as
multi-linestring



However, it is internally different since now when I export as a gpx
file, it is a single segment, which was the goal. Curious that it
still reports the type as MultiLineString.


  Hope it helps,
  

Indeed, it solves the problem
  

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Re: [Qgis-user] Merge does work (at least not as I expect)

[Alexandre Neto]

Hi,

Using your layer directly into merge lines algorithm worked properly on
QGIS 3.4 in Linux. That is, in the end, I got one single feature that is no
longer multi. (if I try to go multipart to single part I can't get the
individual segments).

What does not work (but it's intended) is if you have a layer full of
single segments that connect to each other and try to merge them together
using "merge lines". In that case, I needed to dissolve all layers first,
and then use the merge line tool.

Hope it helps,

Alexandre Neto

On Wed, Oct 2, 2019 at 4:18 PM  wrote:

> On 10/2/2019 12:33 AM, Alexandre Neto wrote:
> > Hi,
> >
> > Can you provide a sample of your data?
> >
> > What version of QGIS are you using? What OS?
> QGIS 3.4.2 on Windows 7 Pro, 64 bit
> Full dataset is attached.
>
>
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Re: [Qgis-user] Merge does work (at least not as I expect)

[qgis-user]

On 10/2/2019 12:33 AM, Alexandre Neto wrote:
> Hi,
>
> Can you provide a sample of your data?
>
> What version of QGIS are you using? What OS?
QGIS 3.4.2 on Windows 7 Pro, 64 bit
Full dataset is attached.

<>
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Re: [Qgis-user] Swamp identification

[Paolo Cavallini]

Alternatively, have a look at it, in processing.
Cheers.

On 2 October 2019 17:57:24 EEST, Jorge Gustavo Rocha  wrote:
>Hi Jean,
>
>Take a look at
>https://fromgistors.blogspot.com/p/semi-automatic-classification-plugin.html
>
>Best regards,
>
>Jorge Gustavo
>
>Às 13:19 de 02/10/19, jean Lukusa escreveu:
>> Hi all .
>> Would you  assist me how to identify swamp areas in a  landsat or
>> googleearth 
>>
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Re: [Qgis-user] Qgis-user] QGIS 3.8 on Debian 10 slow and crashing

[Micha Silver]

Hello all:


Just to complete this thread, I have been working for some months now 
with QGIS 3.8 on Debian 10 running Gnome under X.org (NOT the default 
Wayland). And there have been no issues, no slowdowns, no crashes.


Today, just to test again, I switched back to Gnome under Wayland, and 
immediately got a lock-up in QGIS. And my login session was restarted. 
So there is no doubt that the combination of Gnome+Wayland+QGIS 3.8 does 
not work.



Thanks, Micha



On 22/07/2019 1:08, Raúl Nanclares wrote:
I haven't edited anything yet but I've suffered a couple of crashes ( 
user session restarted) in Debian Buster. I think I've read something 
related in the GitHub issues.

Cheers

El vie., 19 jul. 2019 14:02, > escribió:


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--
Micha Silver
Ben Gurion Univ.
Sde Boker, Remote Sensing Lab
cell: +972-523-665918

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Re: [Qgis-user] Swamp identification

[Jorge Gustavo Rocha]

Hi Jean,

Take a look at
https://fromgistors.blogspot.com/p/semi-automatic-classification-plugin.html

Best regards,

Jorge Gustavo

Às 13:19 de 02/10/19, jean Lukusa escreveu:
> Hi all .
> Would you  assist me how to identify swamp areas in a  landsat or
> googleearth 
>
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[Qgis-user] Swamp identification

[jean Lukusa]

Hi all .
Would you  assist me how to identify swamp areas in a  landsat or
googleearth
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Re: [Qgis-user] Updating multiple parent/child records simultaneously

[McDonaldR]

Hi list,

I've got a project set up in QGIS 3.4.x with a parent polygon layer and a child 
attribute layer.  Each site polygon represents a piece of land and can have 
multiple tasks associated with it (grass cutting, weeding, pruning, etc.).  
Sites can be made up of multiple polygons.

With relations set up in the project it is easy to select a polygon feature and 
update attributes.  It is easy to add or edit associated tasks.  See 
screenshots below.  With multiple site polygons selected I can use the "modify 
selected attributes simultaneously" to update information.

I need to find a way to be able to select site polygons and add the same 
associated task to each one.  For example, select all site polygons that need 
grass cutting task associated with them, assign the task and maintain the 
parent child relationship.  It would be great if there was a way to do this 
through the form.

One solution I have been toying with is using a SQL query to select the site 
polygons and insert into the associated tasks table a new record associated 
with each polygon.  The query works but I need a way to tie it into the form.  
Anyone got any pointers?  Some python to call the SQL and get the selected 
feature IDs from QGIS?

Thanks

Ross

Screenshot 1: https://nextcloud.mixedbredie.net/s/D7DFjs2PrcnEf7t

Screenshot 2: https://nextcloud.mixedbredie.net/s/EBzeTopsBcZBSJc





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Angus House, Orchardbank Business Park, Sylvie Way, Forfar DD8 1AT | t: 01307 
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[QGIS-it-user] Sottogruppi lista layer

[Arrotino]

Buongiorno a tutti,
che voi sappiate esiste un metodo per creare, a partire da un gruppo A, n
sottogruppi in automatico?
Il risultato che vorrei ottenere è il seguente:
GRUPPO A
  sottogruppo 1
  sottogruppo 2
  sottogruppo 3 

Lo chiedo perché ho la necessità di crearne in gran numero in tempo molto
breve.

Grazie a tutti.
Giuseppe 



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Re: [Qgis-user] Merge does work (at least not as I expect)

[Alexandre Neto]

Hi,

Can you provide a sample of your data?

What version of QGIS are you using? What OS?

Alexandre Neto

A quarta, 2/10/2019, 05:03,  escreveu:

> Nyall wrote:
>
> I suspect the lines aren't **exactly** coincident. I'd try:
>
> - multiparts to single parts
> - snap geometries to layer, to snap the end points exactly to each other
> - retry merge
>
>
> I tried this, no joy. still getting multi-linestring with 2055 segments.
> So here's what I tried next -
> multiparts to singlepart
> export to csv, saving geometry as wkt.
> verify that endpoints match *exactly* to the precision written to the file
> Import csv as layer
> merge
>
> again, no luck
>
> I looked at the attribute table and the lines were in some random order-
> adjacent segments were not consecutive rows in the attribute table. Then I
> noticed that every row had the same FID.
> I closed the layer, opened the .csv in excel, verified that the rows
> represented consecutive points, then assigned consecutive FIDs.
> imported csv as layer
> merge
>
> again, no luck. Still have 2055 rows in the attribute table of the merged
> layer, in that same seemingly random order as before.
>
> A purely brute force solution was to export as csv, as above, then edit
> the file by removing the endpoint of each segment, and concatenate them
> into a single linestring with 2055 points.
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[Qgis-user] Request methods

[Mathieu Gillot]

Hello,

In my project I need to compare the result of the concatenation of two
fields, A and B, in common between two different layers.

For he moment, I'm using a calculated field in each layer to concatenate
the two fields. Then a sql request in a virtual layer compare them.

Improving my sql abilities, I noticed that I could do that with a single
virtual layer and a sql request with two sub requests to concatenate the A
and B fields and the primary request to compare them.

My question :

1 - what is the more lightweight solution with large sets of data ?
I noticed that sql requests could seriously slow down qgis. But calculated
fields have to be calculated too...

2 - I do not really master external database solutions yet (I'm using
geopackage and project relations between tables). In fine, is a postgresql
DB could be a solution in term of velocity ? Are the Qgis VL layers have an
equivalent in that kind of database, or must I create them anyway into the
SIG ?

Thanks for any help.

Mathieu G
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