= The `gdal_translate` utility = ''The official documentation for the `gdal_translate` utility is http://www.gdal.org/gdal_translate.html.'' === When to use `-a_ullr` === ''Assign/override the georeferenced bounds of the output file.'' Use the `-a_ullr` option to add coordinates and pixel size to your raster. Using `-a_srs` alone only adds information about coordinate system without modifying the coordinates themselves ( i.e. upper-left coordinates, pixel size and so on). So if the source image doesn't provide this information to gdal they need to be added by hand. == Syntax for PROJ.4 parameters == In trying to use the gdal_translate on a non-standard projection, the hardest part is often to determine what the allowable syntax and meaning of the PROJ.4 parameters were (i.e. `+lat_0=70, +ellps=WGS84`) as an argument to `-a_srs, -t_srs, -s_srs`. There is no clean ready made list, however the [http://www.remotesensing.org/geotiff/proj_list/ GeoTIFF projections transform list] is a great start. Find the page for the projection you need and scan for the '''''PROJ.4 Organization''''' heading. For example this Arcinfo projection: {{{ Projection ALBERS Datum NAD83 Zunits NO Units METERS Spheroid GRS1980 Xshift 0.0000000000 Yshift 0.0000000000 Parameters 61 40 0.000 /* 1st standard parallel 68 0 0.000 /* 2nd standard parallel -132 30 0.000 /* central meridian 59 0 0.000 /* latitude of projection's origin 500000.00000 /* false easting (meters) 500000.00000 /* false northing (meters) }}} Becomes this in PROJ4 [http://www.remotesensing.org/geotiff/proj_list/albers_equal_area_conic.html *]: {{{ +proj=aea +lat_1=61.66666666666666 +lat_2=68.0 +lat_0=59.0 +lon_0=-132.5 +x_0=500000 +y_0=500000 +ellps=GRS80 +datum=NAD83 +units=m }}} If it is a projection you use a lot, write it to a text file and refer to it like this: {{{ gdal_translate ... -t_srs z:\common\yt-albers.proj4 ... infile.tif outfile.tif }}} === Subsetting using -projwin and -outsize === The following uses the -projwin feature to grab a subset of a large tiled WMS (as described on http://www.gdal.org/frmt_wms.html ) {{{ gdal_translate -projwin -20037500 10037500 0 0 -outsize 100 100 frmt_wms_googlemaps_tms.xml junk.png }}}