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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