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I have a number of orthophotos for an area in South Africa, but they are projected in the South African co-ordinate system which measures a location in meters from a central (uneven) meridian. These particular images should use Lo31. However, QGIS does not seem to recognise the South African co-ordinate system and I am battling to display the images correctly. Any ideas how I can solve this dilemma?

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up vote 3 down vote accepted

We hab a similar problem in Namibia here: How do I import specific Coordinates from Namibia in QGis?

I guess your CRS called Lo31 may work the same way. Your CRS should be one of these:

http://spatialreference.org/ref/epsg/2054/

http://spatialreference.org/ref/epsg/22291/

The first one is the current one, they differ by around 300 metres.

Both EPSG codes are incorporated in GDAL 1.9.2 and Qgis Master, so gdalwarp or Raster->Projection->Reproject should do the job. You can work with the reprojeted files in Qgis Lisboa if you prefer that.

EDIT: For gdalwarp commandline processing, you can use one of these:

gdalwarp -s_srs "+proj=tmerc +lat_0=0 +lon_0=31 +k=1 +x_0=0 +y_0=0 +axis=wsu +ellps=WGS84 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs" -t_srs EPSG:3857 -t_srs EPSG:3857 -of GTiff D:/Karten/gdal/gdalwarp/Cape_Lo31.tiff D:/Karten/gdal/gdalwarp/Cape_3857_1.tiff
gdalwarp -s_srs "+proj=tmerc +lat_0=0 +lon_0=31 +k=1 +x_0=0 +y_0=0 +axis=wsu +a=6378249.145 +b=6356514.966398753 +towgs84=-136,-108,-292,0,0,0,0 +units=m +no_defs" -t_srs EPSG:3857 -t_srs EPSG:3857 -of GTiff D:/Karten/gdal/gdalwarp/Cape_Lo31.tiff D:/Karten/gdal/gdalwarp/Cape_3857_2.tiff
gdalwarp -s_srs EPSG:2054 -t_srs EPSG:3857 -of GTiff D:/Karten/gdal/gdalwarp/Cape_Lo31.tiff D:/Karten/gdal/gdalwarp/Cape_3857_3.tiff
gdalwarp -s_srs EPSG:22291 -t_srs EPSG:3857 -of GTiff D:/Karten/gdal/gdalwarp/Cape_Lo31.tiff D:/Karten/gdal/gdalwarp/Cape_3857_4.tiff
pause

First tif is the source, second the target. You can add the proj strings as custom CRS.

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Thank you - you have also confirmed where the problem lies ... I do not have either of these projections installed. Any idea how I can install them? I tried the Co-ordinate Systems Updater plugin, to no avail. The CRS I am looking for is Cape / Lo31. –  Bernie Dec 1 '12 at 16:20
    
Ok, sorry, I see the first link now. Will give that a try. –  Bernie Dec 1 '12 at 17:06
    
Quantum GIS Lisboa and Wroclaw would have the EPSG codes, if installed into a folder without blanks (Thats a known bug, solved in Master). You find them in the share/proj/epsg file. –  Andre Joost Dec 2 '12 at 7:21
    
Thank you, I finally got it right :) –  Bernie Dec 2 '12 at 7:51
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