[GRASS-user] DAtum Warning while using r.in.gdal

[Kim Besson]

Hi Paul

>
> It depends on what the original co-ordinate system of the image was. If it
> was in a different datum from ETRS89 or a different ellipsoid from
> GRS80/WGS84 (which is the datum/ellipsoid of your GRASS location), then
> there will be small errors in the reprojection because you didn't specify a
> datum for the target co-ordinate system.
>
> Gdalinfo from original file I get this:
river: GTiff/GeoTIFF
Files: L71203033_03320001023_B10.TIF
Size is 8141, 7161
Coordinate System is:
PROJCS["WGS 84 / UTM zone 29N",
    GEOGCS["WGS 84",
        DATUM["WGS_1984",
            SPHEROID["WGS 84",6378137,298.257223563,
                AUTHORITY["EPSG","7030"]],
            AUTHORITY["EPSG","6326"]],
        PRIMEM["Greenwich",0],
        UNIT["degree",0.0174532925199433],
        AUTHORITY["EPSG","4326"]],
    PROJECTION["Transverse_Mercator"],
    PARAMETER["latitude_of_origin",0],
    PARAMETER["central_meridian",-9],
    PARAMETER["scale_factor",0.9996],
    PARAMETER["false_easting",500000],
    PARAMETER["false_northing",0],
    UNIT["metre",1,
        AUTHORITY["EPSG","9001"]],
    AUTHORITY["EPSG","32629"]]
Origin = (524400.000000000000000,4414200.000000000000000)
Pixel Size = (30.000000000000000,-30.000000000000000)


I just need to have this data in EPSG:3763 system so I thought that I would
just need to define EPSG:3763 without anything else. Original is in WGS84
and this one is GRS80. What should I do? use in gdalwarp EPSG:3763 or the
PROJ4 extension?
THank you for your help
Kim



> If the two datums are the same (for our purposes it is reasonable to say
> this if the two ellipsoids are the same, or the difference is very small
> (e.g. GRS80 and WGS84)) then there is no problem at all. But in general you
> should specify the datum when doing a reprojection or warping as it can be
> important.
>
>
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