Georaster NODATA in Mapviewer

Question

Hi,
I have a table with few georasters inside and I try to display them on a map in mapviewer.
Everything works fine except one detail: the georasters have some NODATA value. And this NODATA is shown in black on the map (actually it overlaps some data from the other images).
The NODATA attibute is correctly set in my georaster xml.
Does somebody knows a way to avoid displaying the NODATA?
I had a look at the mapviewer documentation and the only work around I found is to define a georaster theme for each individual image and set a polygon_mask in each theme. But it's not convenient at all!
Thanks in advance...
Ganael

Answer 1

Hi Ganael,
you may try to create a colormap for your GeoRaster and assign the alpha value to 0 (which means transparency) for the black pixel. A GeoRaster may have a colormap on the metadata such as:
     <layerID>subLayer1</layerID>
     <colorMap>
       <colors>
         <cell value="0" blue="0" red="0" green="0" alpha="255"/>
         <cell value="1" blue="255" red="255" green="255" alpha="255"/>
         <cell value="2" blue="164" red="0" green="151" alpha="255"/>
    ...Lets say, that the cell value="0" corresponds to your NODATA (black), then you need to make the alpha value = "0". On the GeoRaster documentation you may find some examples of how to set and to get colormap values.
Joao