[Tilecache] problem with transparency of cached tiles

[David Herbert]

Hello,

I am having a few problems getting transparent PNG images to be output
when using Tilecache 1.9rc3.  For example, I have a topography layer
defined thus in tilecache.cfg:

[Topography]
type=WMSLayer
url=http://10.48.1.76:8080/geoserver/wms
layers=sggis:contour_poly
extension=png
bbox=-82000,7800,80000,116000
maxResolution=200.370370
srs=EPSG:2007056

This results in a URL like e.g:

http://10.48.1.76/tilecache/tilecache.cgi?LAYERS=Topography&STYLES=sggis_contour&FORMAT=image%2Fpng&TRANSPARENT=true&SERVICE=WMS&VERSION=1.1.1&REQUEST=GetMap&EXCEPTIONS=application%2Fvnd.ogc.se_inimage&SRS=EPSG%3A2007056&BBOX=20589.62944%2C7800%2C71884.44416%2C59094.81472&WIDTH=256&HEIGHT=256

which appears to be calling the backend Geoserver WMS with
TRANSPARENT=true.  However, the resulting image I get is NOT
transparent.  Calling the backend Geoserver directly thus:

http://10.48.1.76:8080/geoserver/wms/GetMap/?LAYERS=sggis%3Acontour_poly&STYLES=sggis_contour&FORMAT=image%2Fpng&TRANSPARENT=true&SERVICE=WMS&VERSION=1.1.1&REQUEST=GetMap&EXCEPTIONS=application%2Fvnd.ogc.se_inimage&SRS=EPSG%3A2007056&BBOX=20589.62944%2C7800%2C71884.44416%2C59094.81472&WIDTH=256&HEIGHT=256

results in a transparent PNG as expected.  Is this a bug, or have I
missed a vital parameter in tilecache.cfg?

Thanks for any help,

David Herbert
British Antarctic Survey.


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