Some GDAL Functions not working via QGIS interface 3.4.14 Win10

[mattenvsys]

Hi, certain GDAL tools are not working via QGIS Desktop 3.4.14 on Windows 10

For instance, GDAL Polygonise and GDAL Merge do not work

I receive the errors:

C:\PROGRA~1\QGIS3~1.4\bin\python3.exe: No module named gdal_merge
C:\PROGRA~1\QGIS3~1.4\bin\python3.exe: No module named gdal_polygonize

It is effecting all PCs in the office running this version and is reproducible on all raster datasets we have attempted to run.

• Click Raster on the top tool bar
• Select Conversion
• Click Polygonise (Raster to Vector)
• Set the parameters
• Click run

Tool fails instantly

Believe it is something to do with the way QGIS is trying to call/run the command. Here's the initial part of the console call QGIS creates:

python3 -m gdal_polygonize 

Other GDAL tools, susch as GDAL Raster Calculator, work with no issues. Here is and example of the console call for calc:

gdal_calc --calc

QGIS and OS versions

QGIS version 3.4.14-Madeira
QGIS code revision
QGIS code revision
Compiled against Qt 5.11.2
Running against Qt 5.11.2
Compiled against GDAL/OGR 2.4.3
Running against GDAL/OGR 2.4.3
Compiled against GEOS 3.8.0-CAPI-1.13.1
Running against GEOS 3.8.0-CAPI-1.13.1
PostgreSQL Client Version 11.5
SpatiaLite Version 4.3.0
QWT Version 6.1.3
QScintilla2 Version 2.10.8
Compiled against PROJ 5.2.0
Running against PROJ Rel. 5.2.0, September 15th, 2018
Windows 10 Pro

[agiudiceandrea]

Same issue reported on the QGIS-User ML from another user
https://lists.osgeo.org/pipermail/qgis-user/2019-December/044443.html

and another one on StackExchange:
https://gis.stackexchange.com/questions/344713/qgis-3-python-doesnt-find-gdal-module

[agiudiceandrea]

It seems the PYTHONPATH environmental variable is not properly set.
It should be set to the path of the folder where there is gdal_polygonize.py (and the other gdal_*.py python scripts): on Windows with a standalone QGIS 3.4 installation it could be e.g. C:\PROGRA~1\QGIS3~1.4\apps\Python37\Scripts

[gioman]

There is something wrong with the most recent installers,
for example:

QGIS-OSGeo4W-3.4.13-2-Setup-x86_64.exe 11-Nov-2019 16:37 455M
does not show any issue

while

QGIS-OSGeo4W-3.4.13-3-Setup-x86_64.exe 05-Dec-2019 22:06 452M
(as also QGIS-OSGeo4W-3.4.14-1-Setup-x86_64.exe 07-Dec-2019 16:41 452M)
shows the described problems.

@jef-n any idea?

[gioman]

@jef-n any idea?

PS no issues on the latest 3.10

[0verlord84]

I have just installed QGIS ver 3.10.1 but it spits out the same error when I try and run gdal_merge from the GUI.

I have set the PYTHONPATH as C:\Program Files\QGIS 3.10\apps\Python37
GDAL_DATA is at C:\PROGRA~1\QGIS3~1.10\share\gdal
GDAL_DRIVER_PATH is at C:\PROGRA~1\QGIS3~1.10\bin\gdalplugins
PYTHONHOME is the same as PYTHONPATH

The gdal_merge.py (among other gdal modules) are in this folder though (C:\Program Files\QGIS 3.10\apps\Python37\Scripts), which I have tried to point to that path from QGIS as the PYTHONPATH, but unsuccessfully because gdal_merge does not run properly.

I wonder whether it's because I should have installed it via OSGEO4W and point QGIS to those folders instead of the native QGIS ones

[agiudiceandrea]

@0verlord84

The gdal_merge.py (among other gdal modules) are in this folder though (C:\Program Files\QGIS 3.10\apps\Python37\Scripts), which I have tried to point to that path from QGIS as the PYTHONPATH, but unsuccessfully because gdal_merge does not run properly.

This is strange... both the user on the QGIS-User ML and the user on StackExchange have solved the problem [1][2] properly setting the PYTHONPATH environmental variable.

[vizstorylab]

I got the same error, and like a virus, it happened on all the computers in my office. I even installed 3.4 on a brand new computer and got the same error. I clearly remember that it worked well last week. It took me a whole day.

[jef-n]

Fixed in OSGeo4W