[Tilecache] MetaTile causes "Exception: Zero length data returned from layer."

[Matt Bartolome]

On Thu, Aug 6, 2009 at 12:52 PM, Mak Kolybabi<mak.kolybabi at telenium.ca> wrote:
> Whenever I enable MetaTile in TileCache, I cannot seed the cache. If I turn it off, it
> works perfectly.
>
> The error message I receive is:
> % /var/www/tilecache/tilecache_seed.py -f --bbox=133977.89,5427363.5,766071.31,6661918.0 base 0 5
> ###### (0, 17, 0), (2, 21, 0)
> Traceback (most recent call last):
>  File "/var/www/tilecache/tilecache_seed.py", line 9, in <module>
>    TileCache.Client.main()
>  File "/var/www/tilecache/TileCache/Client.py", line 162, in main
>    seed(svc, layer, map(int, args[1:3]), bboxlist , padding=options.padding, force = options.force, reverse = options.reverse)
>  File "/var/www/tilecache/TileCache/Client.py", line 117, in seed
>    svc.renderTile(tile,force=force)
>  File "/var/www/tilecache/TileCache/Service.py", line 140, in renderTile
>    else: raise Exception("Zero length data returned from layer.")

One of your layers is probably empty for the given extent. In the past
I just did this:

else: pass #raise Exception("Zero length data returned from layer.")

Should fix your issue with the seed, but you might want to turn it
back on afterwards so you catch errors you might care about.


> Exception: Zero length data returned from layer.
>
> When I disable MetaTile, it works as expected:
> % /var/www/tilecache/tilecache_seed.py -f --bbox=133977.89,5427363.5,766071.31,6661918.0 base 0 5
> ###### (0, 17, 0), (2, 21, 0)
> Cache miss: -180.0,5370278.0,315724.0,5686182.0, Tile: x: 0, y: 17, z: 0, time: 1.78748202324
> 00 (000000, 000017) = (-180.0000 5370278.0000 315724.0000 5686182.0000) [1.7885s : 0.559/s] 1/8
> ...
>
> My TileCache config is as follows:
> % cat /etc/tilecache.cfg
> [cache]
> type            = Disk
> base            = /var/db/tilecache
>
> [base]
> type            = MapnikLayer
> mapfile         = /var/www/layers/base.lay
> extension       = png
> resolutions     = 1234, 617, 308, 154, 77
> metaTile        = true
>
> [segments]
> type            = MapnikLayer
> mapfile         = /var/www/layers/segments.lay
> extension       = png
> resolutions     = 1234, 617, 308, 154, 77
> metaTile        = true
>
> I've been banging my head against this bug for a couple of hours. I've searched this
> mailing list's archives, as well as Google, and though many other users seem to have
> encountered the problem I'm experiencing, I've not seen any solutions.
>
> Any help you could offer would be very much appreciated.
>
> --
> Mak Kolybabi
> Programmer
> Telenium Inc.
> 204-957-2821
>
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>