[gdal-dev] need help with geo-referencing

Wendell Turner wendell at enflight.com
Wed Feb 17 20:30:04 EST 2010


I'm trying to geo-reference a .tif image, but the
corner coordinates don't change.  I used gimp to get the
pixel and lat/lng of 4 points on the image.  I converted
the lat/lng to the desired coordinates, then used this
command:
  gdal_translate \
   -a_srs epsg:3395 \
   -gcp 1954 1085  -8682920.2818 4766363.8392 0 \
   -gcp 1954 4581  -8682920.2818 4623698.8898 0 \
   -gcp 7376 1085  -8460281.3002 4766363.8392 0 \
   -gcp 7376 4581  -8460281.3002 4623698.8898 0 \
   bw_unref.tif \
   bw_ref.tif

That command produced an output file, but gdalinfo shows the
corner coordinates are still in pixels:
  Corner Coordinates:
  Upper Left  (    0.0,    0.0)
  Lower Left  (    0.0, 5764.0)
  Upper Right ( 7995.0,    0.0)
  Lower Right ( 7995.0, 5764.0)

not the easting/northing that I expect; other files that are
geo-referenced have coordinates like this::
 Corner Coordinates:
  Upper Left  (-8710773.534, 4802386.689) ( 78d15'0.76"W, 39d45'0.87"N)
  Lower Left  (-8710773.534, 4588376.402) ( 78d15'0.76"W, 38d15'0.77"N)
  Upper Right (-8460315.902, 4802386.689) ( 76d 0'1.12"W, 39d45'0.87"N)
  Lower Right (-8460315.902, 4588376.402) ( 76d 0'1.12"W, 38d15'0.77"N)

Also, the coordinate system parameter in the geo-referenced
file is a nicely formatted/indented hierarchy.  In the one I
tried to create it shows as one long string, with `' at the
beginning, as if it isn't really parsed or a part of the
file.

What do I need to do to get the output file to have the
correct coordinate system?

Thanks,

Wendell



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