[gdal-dev] gdalwarp for ED50 UTM zone 31N to WGS84

[Ragi Y. Burhum]

I was just sending this e-mail so that it can be searched through the
archives. Thanks to Even Rouault for walking me through something that
should have been obvious :)

Originally, I was having trouble finding the right parameters for gdalwarp
to be able to warp some imagery that I got from Spain. These were in ED50 /
UTM zone 31N:

rburhum at cuzconix:~/p_bug$ gdalinfo exported_from_original_sid_file.tif
Driver: GTiff/GeoTIFF
Files: exported_from_original_sid_file.tif
Size is 6946, 4800
Coordinate System is:
PROJCS["ED50 / UTM zone 31N",
    GEOGCS["ED50",
        DATUM["European_Datum_1950",
            SPHEROID["International 1924",6378388,297.0000000000014,
                AUTHORITY["EPSG","7022"]],
            AUTHORITY["EPSG","6230"]],
        PRIMEM["Greenwich",0],
        UNIT["degree",0.0174532925199433],
        AUTHORITY["EPSG","4230"]],
    PROJECTION["Transverse_Mercator"],
    PARAMETER["latitude_of_origin",0],
    PARAMETER["central_meridian",3],
    PARAMETER["scale_factor",0.9996],
    PARAMETER["false_easting",500000],
    PARAMETER["false_northing",0],
    UNIT["metre",1,
        AUTHORITY["EPSG","9001"]],
    AUTHORITY["EPSG","23031"]]
Origin = (327720.000000000000000,4730783.500000000000000)
Pixel Size = (0.500000000000000,-0.500000000000000)
Metadata:
  AREA_OR_POINT=Area
Image Structure Metadata:
  INTERLEAVE=PIXEL
Corner Coordinates:
Upper Left  (  327720.000, 4730783.500) (  0d53'46.94"E, 42d42'34.10"N)
Lower Left  (  327720.000, 4728383.500) (  0d53'49.56"E, 42d41'16.35"N)
Upper Right (  331193.000, 4730783.500) (  0d56'19.50"E, 42d42'36.88"N)
Lower Right (  331193.000, 4728383.500) (  0d56'22.08"E, 42d41'19.12"N)
Center      (  329456.500, 4729583.500) (  0d55'4.52"E, 42d41'56.62"N)
Band 1 Block=6946x1 Type=Byte, ColorInterp=Red
Band 2 Block=6946x1 Type=Byte, ColorInterp=Green
Band 3 Block=6946x1 Type=Byte, ColorInterp=Blue


In order to get it to work correctly, I had to use the right +towgs84
parameters from
http://earth-info.nga.mil/GandG/coordsys/onlinedatum/CountryEuropeTable.html.
Although the table showed  -84 (+/-5), -107(+/-6), -120 (+/-3), for my
own
purposes -87, -98, -121 seemed to work best based on my source data.

so the command line would be:

 gdalwarp -s_srs "+proj=utm +zone=31 +ellps=intl +units=m
+towgs84=-87,-101,-121 +no_defs" -t_srs EPSG:4326
exported_from_original_sid_file.tif testout.tif

Hope this helps someone else,

- Ragi
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