I've just started using GeoServer/GeoWebCache to serve map imagery to web
clients which use the TMS service. My source images are in either GeoTIFF or
MrSid format, and are satellite imagery for adjacent areas which slightly
overlap. I have successfully set these up in GeoServer as data sources and
layers, and then made a Layer Group which combines each individual image layer
into a single group so I can easily get tiles for anywhere in the coverage area
via a single TMS request.
My problem is related to nodata areas, which are black in the individual
images, at the borders of each image file where there is an overlap with the
next image. For the GeoTIFF layers, I can easily set the InputTransparentColor
in the GeoServer Layers -> Coverage Parameters screen, and this works great
with the combined layer group correctly serving the actual data rather than the
black pixels for tiles where two images overlap. However, for my MrSid images,
there is no InputTransparentColor option in the Layers screen, and when I get
border tiles with TMS requests I am often getting the black pixels in
preference to the actual data where tiles overlap.
So my question is basically is there any way to set the InputTransparentColor
for layers based on MrSid data sources, or is there something peculiar to this
format that prevent this option from being set?
I also see the same problem if I get a tile layer preview from the web
interface, but interestingly if I ask for a layer preview (rather than a tile
layer preview) the I do not see the problem, and the image layers blend
correctly at the borders. I wonder then if the problem might be related to the
way GeoWebCache requests the images from GeoServer in a way that causes the
nodata to take preference somehow?
System details:
GeoServer 2.2.2 from windows installer
GDAL extensions
Windows XP
Oracle Java 1.7.0_09
Thanks in advance for any help!
Tim
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