spiderplant0,<br><br>1. First, make sure the attribute value field contains a single value for each color, starting from one.<br><br>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.<br>
<br>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'.<br>
<br>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).<br><br>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=<span class="stringliteral">"0"</span> c2=<span class="stringliteral">"0"</span> c3=<span class="stringliteral">"0"</span> c4=<span class="stringliteral">"0"</span>/><br>
<br>4c. For the subsequent values set the alpha value to 255 and the RGB values to show whatever color you need.<br><br>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.<br>
<br>[1]: <a href="http://www.gdal.org/gdal_vrttut.html">http://www.gdal.org/gdal_vrttut.html</a><br><br><div class="gmail_quote">On Wed, May 25, 2011 at 2:58 AM, spiderplant0 <span dir="ltr"><<a href="mailto:spiderplant0@gmail.com">spiderplant0@gmail.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">Hi, Thanks for the reply.<br>
<br>
When I tried this first, the image was displaying just black and white. But<br>
after some experimentation I discovered that '-ot Byte' with gdal_rasterize<br>
gave polygons colored various shades of grey - though not related to my<br>
attribute - seemed to be random.<br>
<br>
I dont understand what you mean by 'If the RGB values are in separate<br>
attributes'. I have one attribute and I want the polygon to be colored<br>
depending on the value of the attribute for this polygon. Eg<br>
if attribute is between 100 and 199 color polygon green<br>
if the attribute is between 200 and 299 color polygon red<br>
etc<br>
(I can change the attribute to discrete integer levels if ranges aren't<br>
allowed).<br>
<br>
I type this:<br>
gdal_rasterize -ts 500 900 -ot Byte -a attributeName -l layerName<br>
vectorFilename.shp rasterFilename.tiff<br>
<br>
Though I'm not sure if this is correct. I guess this is a greyscale image<br>
and not full color. Can't figure out how to get full color.<br>
<br>
Do you know how to add a color table? Is there a gdal utility for this?<br>
<br>
I couldn't find much on the web to explain how to add a color table other<br>
than a suggestion for converting to a .vrt and manually editing the file. I<br>
guess I want a palette raster? But I couldnt figure out the format of the<br>
color table. Or how to specify that the background should be transparent.<br>
<br>
Any clues you can give me would be appreciated.<br>
<font color="#888888"><br>
<br>
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</div></div></blockquote></div><br><br clear="all"><br>-- <br>Best regards,<br>Chaitanya kumar CH.<br>/tʃaɪθənjə/ /kʊmɑr/ <br>+91-9494447584<br>17.2416N 80.1426E<br>