Am Tue, 2 Aug 2011 12:33:20 +0200 schrieb Markus Metz <markus.metz.gisw...@googlemail.com>:
> Otto Dassau: > > Am Mon, 01 Aug 2011 16:24:23 +0200 > > schrieb Even Rouault <even.roua...@mines-paris.org>: > > > >> > > Hi, > >> > > > >> > > I have an elevation map in GRASS with a color table that > >> > > distinguishes decimal values based on the srtm color table, see > >> > > below. I only want to have the value 0 in aqua, and all values <> 0 > >> > > shall reflect land below or above sea level. > >> > > > >> > > -10 57 151 105 > >> > > -0.000001 57 151 105 > >> > > 0 aqua > >> > > 0.000001 57 151 105 > >> > > 50 117 194 93 > >> > > 100 230 230 128 > >> > > 200 202 158 75 > >> > > > >> > > When I export the raster with r.out.gdal (nor now I used GeoTiff and > >> > > ERDAS Img) the color table seems to be changed to reflect "only" > >> > > integer values. so all 0 floating point values are displayed as > >> > > aqua. > >> > > > >> > > Is there a solution for this? > >> > > > >> > > Thanks a lot > >> > > Otto > >> > > >> > Hi, > >> > > >> > fowarded from grass list, because it is probably better here with some > >> > additional notes: > >> > > >> > I used Float32 as data type for the export to ERDAS Img, so the data a > >> > floating point and there is a color table but the colortable does not > >> > reflect the floating point data. > >> > > >> > Color Table (RGB with 174 entries) > >> > 0: 0,191,191,255 > >> > 1: 58,151,105,255 > >> > 2: 59,152,105,255 > >> > 3: 60,153,105,255 > >> > 4: 61,154,105,255 > >> > 5: 62,155,104,255 > >> > 6: 64,156,104,255 > >> > > >> > Is it possible somehow to adjust the colortable after the GRASS export > >> > to get a color table that distinguishes floating point values as it > >> > does in GRASS? > >> > >> Otto, > >> > >> In the GDAL data model, the index of a color table is necessary a > >> (positive) integer. So there's no direct way to translate the GRASS > >> color table of a floating point band into a matching GDAL object. > >> > >> There are several workarounds you could try : > >> * put your color table in a text file that can be used for example by > >> "gdaldem color-relief" . See http://gdal.org/gdaldem.html > >> * build a Raster Attribute Table from the color table and set it to the > >> IMG dataset. But be aware that R.A.T. are rarely exploited by GDAL > >> utilities. > >> > >> > >> Best regards, > >> > >> Even > > > > Thanks a lot Even for your help, > > > > the workaround with gdaldem worked fine for me. I can use the integer > > output for nice looking visualisation in the background and the floating > > ERDAS Img for further processing. > > > > Are there any plans to be able to translate GRASS color tables of a > > floating point band into a matching GDAL object? Would it make sense to > > write an enhancement report to the GDAL bug tracker? > > > AFAIK, color table support depends on the file format and datatype, > nothing that GRASS or GDAL can change. For nice looking visualization, > r.out.tiff or r.out.png would do the job. Otherwise it is probably > safest to export the color rules and supply them as separate text file > together with the exported raster map. > > Markus M Hi Markus, yes, for nice looking visualization r.out.png would be an option, too. I didn't have that in mind - thanks. But r.out.tiff also changes the colors when it changes the values from floating to integer so that's not really an option and I need to come back to some sort of gdaldem workaround. Regards, Otto _______________________________________________ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user