Re: [Qgis-user] creating vector layer from slope map with few classes
Hi Richard, this was great, a big thanks to you as well. Classifying was the first problem, and thanks to your step by step explanation, it worked well, easy, quick, producing exactly the results I wished for. Cheers to you and the community, Maria > Am 30.03.2022 um 20:36 schrieb Richard McDonnell : > > Hi Maria, > There is an option to reclassify a raster called Reclassify by Table, which > should create the classified raster you are looking for. > > You can find the Reclassify by Table in the Processing Toolbox, you can then > do the following. > 1. Select the Raster you want > 2. Under Reclassification table click on the button with the three dots. > a. You need to add a row for each class you want, by clicking Add Row > b. For each row set the Minimum and Maximum pixel Values and the new > Value > c. Click OK once you are happy > 3. Set your output no data value, in your case it can be zero > 4. Set Range boundaries as you require > 5. Set your Output data type, I would, based on your description select > Byte > 6. Set location to which you want to save your Raster. > > To polygonise the data then is just a simple matter of using the QGIS > Polygonize tool, which again can be accessed from the Processing Toolbar. Its > default settings should create the output you are looking for. > Hope the above goes some way to helping you. > > Regards, > > Richard > > > > —— > Richard McDonnell MSc GIS, FME Certified Professional > FRM Data Management > > —— > Oifig na nOibreacha Poiblí > Office of Public Works > > Sráid Jonathan Swift, Baile Átha Troim, Co na Mí, C15 NX36 > Jonathan Swift Street, Trim, Co Meath, C15 NX36 > —— > M +353 87 688 5964 T +353 46 942 2409 > https://gov.ie/opw > > —— > To send me files larger than 30MB, please use the link below > https://filetransfer.opw.ie/filedrop/richard.mcdonn...@opw.ie > > Email Disclaimer: > https://www.gov.ie/en/organisation-information/439daf-email-disclaimer/ > > —— > MSc GIS, FME Certified Professional > > —— > Oifig na nOibreacha Poiblí > Office of Public Works > > Sráid Jonathan Swift, Baile Átha Troim, Co na Mí, C15 NX36 > Jonathan Swift Street, Trim, Co Meath, C15 NX36 > —— > M +353 87 688 5964 T +353 46 942 2409 > https://www.opw.ie > > —— > Email Disclaimer: https://www.opw.ie/en/disclaimer/ >> -Original Message- >> From: Qgis-user On Behalf Of Shinoto, PD >> Dr. Maria via Qgis-user >> Sent: 29 March 2022 22:25 >> To: qgis forum >> Subject: [Qgis-user] creating vector layer from slope map with few classes >> >> Hi, >> >> I have created a slope map from a DTM. >> >> I have limited the symbology to three meaningful classes and wish to create a >> vector layer with polygons of three classes from that. The conditions are >> One- >> Channel-Pseudocolor, Channel1 (Gray), interpolation discrete, modus >> "fortlaufend" -- not identical interval or quantile, 3 classes with values >> <=20, 20 - >> 40, > 40. >> >> The classes show up in the layer design panel symbology tab, but the layer >> browser still (thankfully!) shows the greyscale ramp. >> >> I wish to create a vector layer with polygons from the 3 classes. >> >> All solutions I have looked up work under slightly different condition. >> After all I >> do not know how to get the data of the DTM into three classes like >> "Flat-Gentle- >> Steep"; I think the vectorization should work easily then. >> >> Can anybody hint me to a solution? >> >> >> Thanks and best wishes, >> Maria >> ___ >> Qgis-user mailing list >> Qgis-user@lists.osgeo.org >> List info: https://lists.osgeo.org/mailman/listinfo/qgis-user >> Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user ___ Qgis-user mailing list Qgis-user@lists.osgeo.org List info: https://lists.osgeo.org/mailman/listinfo/qgis-user Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user
Re: [Qgis-user] creating vector layer from slope map with few classes
Hi,
Thanks for your advice and offer to help. Yesterday, I had a QGIS crash, today,
I restarted, and the problems with polygonize (GDAL and QGIS) were gone.
Yesterday I could not create a virtual layer and no stored layer, today, both
are no problems. Sorry for causing trouble -- but I have to say, that gave a
lot of confidence.
I still have some warnings, particularly with Python code involved (I do not
yet use it myself directly). But I will solve these step by step, for the time
being: Polygonize is not a problem any more.
Cheers, and thanks as always,
Maria
> Am 30.03.2022 um 19:54 schrieb Nicolas Cadieux :
>
> Hi,
>
> If you’re comfortable with python you can always follow the introduction here.
>
> https://pcjericks.github.io/py-gdalogr-cookbook/raster_layers.html#polygonize-a-raster-band
>
> You can also send me a link to the file and I could try on a windows box.
> You could check bug reports to see if it’s been reported also.
>
> Nicolas Cadieux
> https://gitlab.com/njacadieux
>
>> Le 29 mars 2022 à 21:04, Shinoto, PD Dr. Maria
>> a écrit :
>>
>> Nicolas,
>>
>> Tried it once again, short names and reasonable paths do not work. I am on
>> Mac, QGIS 3.24, will test some reasons for the failure tomorrow again and
>> report. Thanks for your advice,
>>
>> Maria
>>
>>
>>
>>> Am 30.03.2022 um 09:34 schrieb Nicolas Cadieux via Qgis-user
>>> :
>>>
>>> Hi,
>>>
>>> "Polygonize" should work well to vectorize the raster classes. If you have
>>> problems with the file name, try simplifying the file name to the bare
>>> minimun like c:\temp\toto.shp if you're on Windows. Make sure you have no
>>> spaces or accents in the path (this includes the user path of your
>>> operation system). Notice that there are two polygonize algorithm. One is
>>> from QGIS and one is from GDAL. Try both. They are probably both based
>>> on GDAL but one (probably the QGIS one) may have an easier time with
>>> accents, spaces or special characters like '\n'.
>>>
>>> Good luck
>>>
>>> Nicolas
>>>
>>> On 2022-03-29 7:51 p.m., Shinoto, PD Dr. Maria via Qgis-user wrote:
>>>> Hi Kirk,
>>>>
>>>> that was helpful, thank you.
>>>>
>>>> I am not yet where I need to be, but so far I could create two classes
>>>> with the formula found in the docs
>>>> (https://docs.qgis.org/3.10/en/docs/user_manual/working_with_raster/raster_analysis.html)
>>>> along this line:
>>>>
>>>> `("slope@1" < 50) * 1 + ("slope@1" >= 50) * 2`
>>>>
>>>> At this moment, my biggest problem is creating the vector file, the window
>>>> claims that the file name is too long. This cannot be the case, and the
>>>> directory itself should be OK. So now I am trying to get this done, and
>>>> then I will test three classes, which I did not get working up to now
>>>> either.
>>>>
>>>> If there are easy answers to these two questions, I would be pleased,
>>>> otherwise, I will try tomorrow.
>>>>
>>>> Thanks a lot,
>>>> Maria
>>>>
>>>>
>>>>
>>>>> Am 30.03.2022 um 07:14 schrieb kirk :
>>>>>
>>>>> Hi Maria.
>>>>> The symbology does not reclassify the underlying raster, it just changes
>>>>> the way it is displayed. Use the raster calculator to generate a new
>>>>> raster with the Classes you require. The native qgis calculator works
>>>>> well. You can find it in the upper word menu under raster. Once you
>>>>> have your raster reclassified, you can then convert it to a vector format
>>>>>
>>>>> Kirk Schmidt
>>>>>
>>>>>
>>>>>
>>>>> Sent from my Galaxy
>>>>>
>>>>>
>>>>> Original message
>>>>> From: "Shinoto, PD Dr. Maria via Qgis-user"
>>>>> Date: 2022-03-29 6:32 p.m. (GMT-04:00)
>>>>> To: qgis forum
>>>>> Subject: [Qgis-user] creating vector layer from slope map with few classes
>>>>>
>>>>> Hi,
>>>>>
>>>>> I have created a slope map from a DTM.
>>>>>
>>>>> I have limited the symbology to three meaningful classes and wish to
>>>>> crea
Re: [Qgis-user] creating vector layer from slope map with few classes
Hi,
If you’re comfortable with python you can always follow the introduction here.
https://pcjericks.github.io/py-gdalogr-cookbook/raster_layers.html#polygonize-a-raster-band
You can also send me a link to the file and I could try on a windows box. You
could check bug reports to see if it’s been reported also.
Nicolas Cadieux
https://gitlab.com/njacadieux
> Le 29 mars 2022 à 21:04, Shinoto, PD Dr. Maria
> a écrit :
>
> Nicolas,
>
> Tried it once again, short names and reasonable paths do not work. I am on
> Mac, QGIS 3.24, will test some reasons for the failure tomorrow again and
> report. Thanks for your advice,
>
> Maria
>
>
>
>> Am 30.03.2022 um 09:34 schrieb Nicolas Cadieux via Qgis-user
>> :
>>
>> Hi,
>>
>> "Polygonize" should work well to vectorize the raster classes. If you have
>> problems with the file name, try simplifying the file name to the bare
>> minimun like c:\temp\toto.shp if you're on Windows. Make sure you have no
>> spaces or accents in the path (this includes the user path of your operation
>> system). Notice that there are two polygonize algorithm. One is from QGIS
>> and one is from GDAL. Try both. They are probably both based on GDAL but
>> one (probably the QGIS one) may have an easier time with accents, spaces or
>> special characters like '\n'.
>>
>> Good luck
>>
>> Nicolas
>>
>>> On 2022-03-29 7:51 p.m., Shinoto, PD Dr. Maria via Qgis-user wrote:
>>> Hi Kirk,
>>>
>>> that was helpful, thank you.
>>>
>>> I am not yet where I need to be, but so far I could create two classes with
>>> the formula found in the docs
>>> (https://docs.qgis.org/3.10/en/docs/user_manual/working_with_raster/raster_analysis.html)
>>> along this line:
>>>
>>>`("slope@1" < 50) * 1 + ("slope@1" >= 50) * 2`
>>>
>>> At this moment, my biggest problem is creating the vector file, the window
>>> claims that the file name is too long. This cannot be the case, and the
>>> directory itself should be OK. So now I am trying to get this done, and
>>> then I will test three classes, which I did not get working up to now
>>> either.
>>>
>>> If there are easy answers to these two questions, I would be pleased,
>>> otherwise, I will try tomorrow.
>>>
>>> Thanks a lot,
>>> Maria
>>>
>>>
>>>
>>>> Am 30.03.2022 um 07:14 schrieb kirk :
>>>>
>>>> Hi Maria.
>>>> The symbology does not reclassify the underlying raster, it just changes
>>>> the way it is displayed. Use the raster calculator to generate a new
>>>> raster with the Classes you require. The native qgis calculator works
>>>> well. You can find it in the upper word menu under raster. Once you have
>>>> your raster reclassified, you can then convert it to a vector format
>>>>
>>>> Kirk Schmidt
>>>>
>>>>
>>>>
>>>> Sent from my Galaxy
>>>>
>>>>
>>>> Original message
>>>> From: "Shinoto, PD Dr. Maria via Qgis-user"
>>>> Date: 2022-03-29 6:32 p.m. (GMT-04:00)
>>>> To: qgis forum
>>>> Subject: [Qgis-user] creating vector layer from slope map with few classes
>>>>
>>>> Hi,
>>>>
>>>> I have created a slope map from a DTM.
>>>>
>>>> I have limited the symbology to three meaningful classes and wish to
>>>> create a vector layer with polygons of three classes from that. The
>>>> conditions are One-Channel-Pseudocolor, Channel1 (Gray), interpolation
>>>> discrete, modus "fortlaufend" -- not identical interval or quantile, 3
>>>> classes with values <=20, 20 - 40, > 40.
>>>>
>>>> The classes show up in the layer design panel symbology tab, but the layer
>>>> browser still (thankfully!) shows the greyscale ramp.
>>>>
>>>> I wish to create a vector layer with polygons from the 3 classes.
>>>>
>>>> All solutions I have looked up work under slightly different condition.
>>>> After all I do not know how to get the data of the DTM into three classes
>>>> like "Flat-Gentle-Steep"; I think the vectorization should work easily
>>>> then.
>>>>
>>>> Can anybody hint me to a solution?
>>>>
>>>>
>>&g
Re: [Qgis-user] creating vector layer from slope map with few classes
Nicolas,
Tried it once again, short names and reasonable paths do not work. I am on Mac,
QGIS 3.24, will test some reasons for the failure tomorrow again and report.
Thanks for your advice,
Maria
> Am 30.03.2022 um 09:34 schrieb Nicolas Cadieux via Qgis-user
> :
>
> Hi,
>
> "Polygonize" should work well to vectorize the raster classes. If you have
> problems with the file name, try simplifying the file name to the bare
> minimun like c:\temp\toto.shp if you're on Windows. Make sure you have no
> spaces or accents in the path (this includes the user path of your operation
> system). Notice that there are two polygonize algorithm. One is from QGIS
> and one is from GDAL. Try both. They are probably both based on GDAL but
> one (probably the QGIS one) may have an easier time with accents, spaces or
> special characters like '\n'.
>
> Good luck
>
> Nicolas
>
> On 2022-03-29 7:51 p.m., Shinoto, PD Dr. Maria via Qgis-user wrote:
>> Hi Kirk,
>>
>> that was helpful, thank you.
>>
>> I am not yet where I need to be, but so far I could create two classes with
>> the formula found in the docs
>> (https://docs.qgis.org/3.10/en/docs/user_manual/working_with_raster/raster_analysis.html)
>> along this line:
>>
>> `("slope@1" < 50) * 1 + ("slope@1" >= 50) * 2`
>>
>> At this moment, my biggest problem is creating the vector file, the window
>> claims that the file name is too long. This cannot be the case, and the
>> directory itself should be OK. So now I am trying to get this done, and then
>> I will test three classes, which I did not get working up to now either.
>>
>> If there are easy answers to these two questions, I would be pleased,
>> otherwise, I will try tomorrow.
>>
>> Thanks a lot,
>> Maria
>>
>>
>>
>>> Am 30.03.2022 um 07:14 schrieb kirk :
>>>
>>> Hi Maria.
>>> The symbology does not reclassify the underlying raster, it just changes
>>> the way it is displayed. Use the raster calculator to generate a new
>>> raster with the Classes you require. The native qgis calculator works well.
>>> You can find it in the upper word menu under raster. Once you have your
>>> raster reclassified, you can then convert it to a vector format
>>>
>>> Kirk Schmidt
>>>
>>>
>>>
>>> Sent from my Galaxy
>>>
>>>
>>> Original message
>>> From: "Shinoto, PD Dr. Maria via Qgis-user"
>>> Date: 2022-03-29 6:32 p.m. (GMT-04:00)
>>> To: qgis forum
>>> Subject: [Qgis-user] creating vector layer from slope map with few classes
>>>
>>> Hi,
>>>
>>> I have created a slope map from a DTM.
>>>
>>> I have limited the symbology to three meaningful classes and wish to create
>>> a vector layer with polygons of three classes from that. The conditions are
>>> One-Channel-Pseudocolor, Channel1 (Gray), interpolation discrete, modus
>>> "fortlaufend" -- not identical interval or quantile, 3 classes with values
>>> <=20, 20 - 40, > 40.
>>>
>>> The classes show up in the layer design panel symbology tab, but the layer
>>> browser still (thankfully!) shows the greyscale ramp.
>>>
>>> I wish to create a vector layer with polygons from the 3 classes.
>>>
>>> All solutions I have looked up work under slightly different condition.
>>> After all I do not know how to get the data of the DTM into three classes
>>> like "Flat-Gentle-Steep"; I think the vectorization should work easily then.
>>>
>>> Can anybody hint me to a solution?
>>>
>>>
>>> Thanks and best wishes,
>>> Maria
>>> ___
>>> Qgis-user mailing list
>>> Qgis-user@lists.osgeo.org
>>> List info: https://lists.osgeo.org/mailman/listinfo/qgis-user
>>> Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user
>>>
>> ___
>> Qgis-user mailing list
>> Qgis-user@lists.osgeo.org
>> List info: https://lists.osgeo.org/mailman/listinfo/qgis-user
>> Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user
>
> --
> Nicolas Cadieux
> https://gitlab.com/njacadieux
>
> ___
> Qgis-user mailing list
> Qgis-user@lists.osgeo.org
> List info: https://lists.osgeo.org/mailman/listinfo/qgis-user
> Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user
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Re: [Qgis-user] creating vector layer from slope map with few classes
Hi,
"Polygonize" should work well to vectorize the raster classes. If you
have problems with the file name, try simplifying the file name to the
bare minimun like c:\temp\toto.shp if you're on Windows. Make sure you
have no spaces or accents in the path (this includes the user path of
your operation system). Notice that there are two polygonize
algorithm. One is from QGIS and one is from GDAL. Try both. They are
probably both based on GDAL but one (probably the QGIS one) may have an
easier time with accents, spaces or special characters like '\n'.
Good luck
Nicolas
On 2022-03-29 7:51 p.m., Shinoto, PD Dr. Maria via Qgis-user wrote:
Hi Kirk,
that was helpful, thank you.
I am not yet where I need to be, but so far I could create two classes with the
formula found in the docs
(https://docs.qgis.org/3.10/en/docs/user_manual/working_with_raster/raster_analysis.html)
along this line:
`("slope@1" < 50) * 1 + ("slope@1" >= 50) * 2`
At this moment, my biggest problem is creating the vector file, the window
claims that the file name is too long. This cannot be the case, and the
directory itself should be OK. So now I am trying to get this done, and then I
will test three classes, which I did not get working up to now either.
If there are easy answers to these two questions, I would be pleased,
otherwise, I will try tomorrow.
Thanks a lot,
Maria
Am 30.03.2022 um 07:14 schrieb kirk :
Hi Maria.
The symbology does not reclassify the underlying raster, it just changes the
way it is displayed. Use the raster calculator to generate a new raster with
the Classes you require. The native qgis calculator works well. You can find it
in the upper word menu under raster. Once you have your raster reclassified,
you can then convert it to a vector format
Kirk Schmidt
Sent from my Galaxy
Original message
From: "Shinoto, PD Dr. Maria via Qgis-user"
Date: 2022-03-29 6:32 p.m. (GMT-04:00)
To: qgis forum
Subject: [Qgis-user] creating vector layer from slope map with few classes
Hi,
I have created a slope map from a DTM.
I have limited the symbology to three meaningful classes and wish to create a vector layer with
polygons of three classes from that. The conditions are One-Channel-Pseudocolor, Channel1
(Gray), interpolation discrete, modus "fortlaufend" -- not identical interval or
quantile, 3 classes with values <=20, 20 - 40, > 40.
The classes show up in the layer design panel symbology tab, but the layer
browser still (thankfully!) shows the greyscale ramp.
I wish to create a vector layer with polygons from the 3 classes.
All solutions I have looked up work under slightly different condition. After all I do
not know how to get the data of the DTM into three classes like
"Flat-Gentle-Steep"; I think the vectorization should work easily then.
Can anybody hint me to a solution?
Thanks and best wishes,
Maria
___
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--
Nicolas Cadieux
https://gitlab.com/njacadieux
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Re: [Qgis-user] creating vector layer from slope map with few classes
Hi Kirk,
that was helpful, thank you.
I am not yet where I need to be, but so far I could create two classes with the
formula found in the docs
(https://docs.qgis.org/3.10/en/docs/user_manual/working_with_raster/raster_analysis.html)
along this line:
`("slope@1" < 50) * 1 + ("slope@1" >= 50) * 2`
At this moment, my biggest problem is creating the vector file, the window
claims that the file name is too long. This cannot be the case, and the
directory itself should be OK. So now I am trying to get this done, and then I
will test three classes, which I did not get working up to now either.
If there are easy answers to these two questions, I would be pleased,
otherwise, I will try tomorrow.
Thanks a lot,
Maria
> Am 30.03.2022 um 07:14 schrieb kirk :
>
> Hi Maria.
> The symbology does not reclassify the underlying raster, it just changes the
> way it is displayed. Use the raster calculator to generate a new raster with
> the Classes you require. The native qgis calculator works well. You can find
> it in the upper word menu under raster. Once you have your raster
> reclassified, you can then convert it to a vector format
>
> Kirk Schmidt
>
>
>
> Sent from my Galaxy
>
>
> Original message
> From: "Shinoto, PD Dr. Maria via Qgis-user"
> Date: 2022-03-29 6:32 p.m. (GMT-04:00)
> To: qgis forum
> Subject: [Qgis-user] creating vector layer from slope map with few classes
>
> Hi,
>
> I have created a slope map from a DTM.
>
> I have limited the symbology to three meaningful classes and wish to create a
> vector layer with polygons of three classes from that. The conditions are
> One-Channel-Pseudocolor, Channel1 (Gray), interpolation discrete, modus
> "fortlaufend" -- not identical interval or quantile, 3 classes with values
> <=20, 20 - 40, > 40.
>
> The classes show up in the layer design panel symbology tab, but the layer
> browser still (thankfully!) shows the greyscale ramp.
>
> I wish to create a vector layer with polygons from the 3 classes.
>
> All solutions I have looked up work under slightly different condition. After
> all I do not know how to get the data of the DTM into three classes like
> "Flat-Gentle-Steep"; I think the vectorization should work easily then.
>
> Can anybody hint me to a solution?
>
>
> Thanks and best wishes,
> Maria
> ___
> Qgis-user mailing list
> Qgis-user@lists.osgeo.org
> List info: https://lists.osgeo.org/mailman/listinfo/qgis-user
> Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user
>
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Re: [Qgis-user] creating vector layer from slope map with few classes
Hi Maria.The symbology does not reclassify the underlying raster, it just changes the way it is displayed. Use the raster calculator to generate a new raster with the Classes you require. The native qgis calculator works well. You can find it in the upper word menu under raster. Once you have your raster reclassified, you can then convert it to a vector format Kirk SchmidtSent from my Galaxy Original message From: "Shinoto, PD Dr. Maria via Qgis-user" Date: 2022-03-29 6:32 p.m. (GMT-04:00) To: qgis forum Subject: [Qgis-user] creating vector layer from slope map with few classes Hi, I have created a slope map from a DTM. I have limited the symbology to three meaningful classes and wish to create a vector layer with polygons of three classes from that. The conditions are One-Channel-Pseudocolor, Channel1 (Gray), interpolation discrete, modus "fortlaufend" -- not identical interval or quantile, 3 classes with values <=20, 20 - 40, > 40. The classes show up in the layer design panel symbology tab, but the layer browser still (thankfully!) shows the greyscale ramp. I wish to create a vector layer with polygons from the 3 classes. All solutions I have looked up work under slightly different condition. After all I do not know how to get the data of the DTM into three classes like "Flat-Gentle-Steep"; I think the vectorization should work easily then. Can anybody hint me to a solution?Thanks and best wishes, Maria___Qgis-user mailing listQgis-user@lists.osgeo.orgList info: https://lists.osgeo.org/mailman/listinfo/qgis-userUnsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user___ Qgis-user mailing list Qgis-user@lists.osgeo.org List info: https://lists.osgeo.org/mailman/listinfo/qgis-user Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user
[Qgis-user] creating vector layer from slope map with few classes
Hi, I have created a slope map from a DTM. I have limited the symbology to three meaningful classes and wish to create a vector layer with polygons of three classes from that. The conditions are One-Channel-Pseudocolor, Channel1 (Gray), interpolation discrete, modus "fortlaufend" -- not identical interval or quantile, 3 classes with values <=20, 20 - 40, > 40. The classes show up in the layer design panel symbology tab, but the layer browser still (thankfully!) shows the greyscale ramp. I wish to create a vector layer with polygons from the 3 classes. All solutions I have looked up work under slightly different condition. After all I do not know how to get the data of the DTM into three classes like "Flat-Gentle-Steep"; I think the vectorization should work easily then. Can anybody hint me to a solution? Thanks and best wishes, Maria ___ Qgis-user mailing list Qgis-user@lists.osgeo.org List info: https://lists.osgeo.org/mailman/listinfo/qgis-user Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user
