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

[Bill Woodall]

On Thu, 2007-01-25 at 10:45 -0700, Corey Puffalt wrote:
> 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


Hi Corey,

I don't use GeoServer, but MapServer and I think that GeoServer
currently is WFS (with WMS in the future 2.0 release ) 
and tileCache is setup to handle WMS or TMS requests.

$.02

........Bill,
OL/TC User