spiderplant0, 1. First, make sure the attribute value field contains a single value for each color, starting from one.
2. Run gdal_rasterize after adding the option '-init 0' to your original options. This option makes sure that the background pixels are initialized to zero. You will get a greyscale image. 3. The best way to color this image using gdal utilities is by using a .vrt file. You may also be able to do this using an image editor like GIMP. Run gdalbuildvrt with the option '-srcnodata 0' to create a VRT named, say, 'output.vrt'. 4a. Refer to the GDAL VRT tutorial [1] and add ColorTable element inside the VRTRasterband element. It should be at the same level as the NoDataValue element (Which should contain the value 0 here). 4b. For the first Entry, which interprets the value 0, set the alpha value (c4) to 0 to make it transparent. i.e. <Entry c1="0" c2="0" c3="0" c4="0"/> 4c. For the subsequent values set the alpha value to 255 and the RGB values to show whatever color you need. 5. Run gdal_translate on output.vrt with the option "-expand rgba". The output raster will contain the colors you specified in the ColorTable with the background transparent. [1]: http://www.gdal.org/gdal_vrttut.html On Wed, May 25, 2011 at 2:58 AM, spiderplant0 <[email protected]>wrote: > Hi, Thanks for the reply. > > When I tried this first, the image was displaying just black and white. But > after some experimentation I discovered that '-ot Byte' with gdal_rasterize > gave polygons colored various shades of grey - though not related to my > attribute - seemed to be random. > > I dont understand what you mean by 'If the RGB values are in separate > attributes'. I have one attribute and I want the polygon to be colored > depending on the value of the attribute for this polygon. Eg > if attribute is between 100 and 199 color polygon green > if the attribute is between 200 and 299 color polygon red > etc > (I can change the attribute to discrete integer levels if ranges aren't > allowed). > > I type this: > gdal_rasterize -ts 500 900 -ot Byte -a attributeName -l layerName > vectorFilename.shp rasterFilename.tiff > > Though I'm not sure if this is correct. I guess this is a greyscale image > and not full color. Can't figure out how to get full color. > > Do you know how to add a color table? Is there a gdal utility for this? > > I couldn't find much on the web to explain how to add a color table other > than a suggestion for converting to a .vrt and manually editing the file. I > guess I want a palette raster? But I couldnt figure out the format of the > color table. Or how to specify that the background should be transparent. > > Any clues you can give me would be appreciated. > > > -- > View this message in context: > http://osgeo-org.1803224.n2.nabble.com/Convert-vector-to-raster-with-colored-polygons-tp6396185p6400545.html > Sent from the GDAL - Dev mailing list archive at Nabble.com. > _______________________________________________ > gdal-dev mailing list > [email protected] > http://lists.osgeo.org/mailman/listinfo/gdal-dev > -- Best regards, Chaitanya kumar CH. /tʃaɪθənjə/ /kʊmɑr/ +91-9494447584 17.2416N 80.1426E
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