I am trying to obtain elevation readings using gdallocationinfo (as per other datasets I have) from a set of .asc files containing elevation data (plus an associated .prj file), using WGS84, but I can't seem to find a way to do this in a way that uses the correct projection.

gdal_merge.py -o ../osTerrain50.tiff *.asc

gives me a GeoTIFF.

Opening this in QGIS shows that the data appears correctly, but it does ask me for the projection, so I specify EPSG:27700 (which is OSGB36).

Indeed gdalinfo does show that the .tiff file doesn't end up containing the projection:

> gdalinfo osTerrain50.tiff

Driver: GTiff/GeoTIFF
Files: osTerrain50.tiff
Size is 13200, 24600
Coordinate System is `'
Origin = (0.000000000000000,1230000.000000000000000)
Pixel Size = (50.000000000000000,-50.000000000000000)
Image Structure Metadata:
Corner Coordinates:
Upper Left  (       0.000, 1230000.000) 
Lower Left  (   0.0000000,   0.0000000) 
Upper Right (  660000.000, 1230000.000) 
Lower Right (  660000.000,       0.000) 
Center      (  330000.000,  615000.000) 
Band 1 Block=13200x1 Type=Float32, ColorInterp=Gray

What do I need to do reproject this to WGS84, into some format (TIFF/shp/whatever) that gdallocationinfo can read?

NB I need to do this via the command-line, not via GUI programs.

  • I think you need to merge the reproject using gdal_transform – Ian Turton Jan 15 '16 at 20:42
  • Or create a VRT and reproject that and then convert to a tiff – Ian Turton Jan 15 '16 at 20:42

If QGIS asks you for a CRS, it does not write that information into the file. You have to save the data into a new file, then QGIS writes the CRS information into it.

Alternatively, use gdal_translate -a_srs to assign the CRS to the output file.

If you need a different projection, use gdalwarp -s_srs -t_srs to do both things in one step.

  • Thanks; that worked: gdal_translate -a_srs "EPSG:27700" osTerrain50.tiff osTerrain50_osgb36.tiff – fooquency Jan 16 '16 at 18:04
  • And the second worked: gdalwarp -s_srs "EPSG:27700" -t_srs "EPSG:4326" osTerrain50.tiff osTerrain50_wgs84.tiff – fooquency Jan 16 '16 at 18:04

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