[OpenLayers-Users] OT: TileCache problems...

[Corey Puffalt]

Hi...

I've been unable to find a mailing list dedicated to TileCache (
http://labs.metacarta.com/wms-c/) but I've noticed other people posting
questions about it here as well so I hope no one minds.

I'm trying to get a system working with an OpenLayers front end, GeoServer
on the backend with a tile cache in the middle.  I chose TileCache because
of its nifty meta-tiling feature which makes labelled layers look *much*
better (by turning the 256x256px OpenLayers tile requests into larger
requests).

OpenLayers and GeoServer work just fine together but once I add TileCache to
the equation things get nutty:

a) My first issue is that some of the tiles outside the normal bbox of my
layer are rendered strangely.  The first tile to the left of the bbox of the
layer appears to be a duplicate of the one to the right.  The tiles below
the normal bbx of the layer appear to be duplicates (for the most part) of
the tiles above.  This behavior persists with metaTiling on or off.
Everything looks fine without TileCache.

b) The second issue is that with metaTile=true I start seeing broken
images.  Some tiles render fine (though with the same problem above when
outside the bbox boundary) but others are broken.  The error that TileCache
reports for the broken images is:

An error occurred: Zero length data returned from layer.
  File "/stuff/tilecache-1.3/TileCache/Service.py", line 399, in
modPythonHandler
    host )

  File "/stuff/tilecache-1.3/TileCache/Service.py", line 384, in dispatchRequest
    return self.renderTile(tile, params.has_key('FORCE'))

  File "/stuff/tilecache-1.3/TileCache/Service.py", line 363, in renderTile
    else: raise Exception("Zero length data returned from layer.")

I added some debug statements to the TileCache code in order to determine
the actual map request it was making to GeoServer.  When I make the same
request to GeoServer it returns the image just fine so I'm not sure what the
actual problem is.

The URLs being generated by TileCache with metatiling turned on weren't
quite what I was expecting.  Specifically the width and height are strange
values.  I'm using 256x256px tiles and using the default meta* options in
TileCache and it's turning my 256x256px tile requests into requests of
1300x532px size.  Can anyone explain that to me?

Here's the tilecache.cfg file I'm using (note the custom resolutions due to
me using a maxResolution setting of 0.5625 in openlayers):

[cache]
type=DiskCache
base=/tmp/tilecache

[basemap]
type=WMSLayer
url=http://maphost:8081/geoserver/wms?BGCOLOR=0x7391AD
extension=gif
resolutions=0.5625,0.28125,0.140625,0.0703125,0.03515625,0.017578125,
0.008789062,0.004394531,0.002197266,0.001098633,0.000549316,0.000274658,
0.000137329
metaTile=true


Any help would be much appreciated.

Regards,
Corey
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.osgeo.org/pipermail/openlayers-users/attachments/20070125/5e472f17/attachment.html