My aim was
to show some elevation data from geotiffs as the user moved the mouse.
The elevation data is served from geoserver. If you think it as normal
WMS raster images you will be in trouble. In geoserver raw data is
transformed to something "rasterable", so in udig. Your raw data is
mapped to 0-255 values. To overcome this i have used some plugin from
nasa worldwind forums which lets geoserver wms serve raw data to
clients. I changed this to serve custom geotiffs. Then a developed a
custom renderer in udig which requests this image format rather than
standard wms formats like png. This custom renderer also holds a pointer
to the gridcoverage which later helps me to evaluate the elevation data
at the mouse cursor position.
One of the key points is to tell udig request a custom format from wms
for a specific layer and dont change the requests for other layers. I
have accomplished this using layer blackboard and injecting some
variable to check on the renderer side,