QGIS » QGIS Application

The way to test with GDAL is to use gdalsrsinfo:

gdalsrsinfo epsg:2950 -o proj4
'+proj=tmerc +lat_0=0 +lon_0=-73.5 +k=0.9999 +x_0=304800 +y_0=0 +ellps=GRS80 +to
wgs84=0,0,0,0,0,0,0 +units=m +no_defs '

gdalsrsinfo epsg:32188 -o proj4
'+proj=tmerc +lat_0=0 +lon_0=-73.5 +k=0.9999 +x_0=304800 +y_0=0 +ellps=GRS80 +to
wgs84=0,0,0,0,0,0,0 +units=m +no_defs '

Prj and WKT outputs are different in GEOGCS NAD83 vs. GEOGCS NAD83 (CSRS). You can change the projection code also from layer-properties, but does the change have any effect it the nadgrid file to use is not defined and also available to GDAL and QGIS?

Thanks for the information.

Yes, indeed, it is possible to manually correct the files projections by one or other of manipulation as possible. It's like fix something with tape that is not working as it should.

However, it would be perfect if Qgis could open the files with good projection automatically without anyone having to worry about it.

I do not know these projections at all, but I wonder it your fix by fiddling with the qpj files does really have any effect. The projections are basically the same. The only difference, if I understand it right, is that the one named NAD83 (CSRS) is newer and does not have local distortions which are corrected in the older projection with a nadgrids file. My GDAL 2.0 from gisinternals does not have nadgrid files defined for either of the projections which makes them to be just the same for GDAL.

I tested that ogrinfo finds different projections from your sample files. Then I made a test with gdaltransform:

gdaltransform -s_srs epsg:2950 -t_srs epsg:4326
313658.844100 5026941.160835
-73.3868787673789 45.3823557428898 0

gdaltransform -s_srs epsg:32188 -t_srs epsg:4326
313658.844100, 5026941.160835
-73.3868787673789 45.3823557428898 0

Same coordinates for both 2950 and 32188 which means that if you do not have correct gridshift files and adjusted Proj4 definitions for the projections you can as well use 2950 or 32188 throughout, or a mixture of both, because the end result will still be the same.

Do you have the nadgrid files "tnhpgn.las" for epsg:32188 as documented in http://epsg.io/32188-1733 ? It seems that 2950 does not need gridshift files http://epsg.io/2950.

As I said, I have no experience on these projections and I may be all wrong.

I believe there are two issues. First one it that after reading data in EPSG:2950 and EPSG:32188 they do not distinguish. Another issue is that if you convert data from for example EPSG:4326 into 2950 or 32188 the result will be identical because QGIS/GDAL/Proj4 does not come with the "tnhpgn.las" file or something equivalent. I do not know if the format of that .las file is correct for those.

I do not know how to make custom CRS to utilize nadgrids with QGIS. Reading this ticket and the related ones may give some information #2913. I think that myself, if the accuracy counts, I would select either 2950 or 32188 and convert all my data into that with ogr2ogr. It understands nadgrids in Proj strings.

Hi,

Thank you for your solutions.
For now , since the files arrive one by one, the simplest method of correction remains to copy and paste a good QPJ then rename it as the new file received.
The geometry need not be reprojected because it is already in MTM Nad 83.