[Tilecache] troubleshooting for tilecache

[Paul Spencer]

A few things that may be useful to note in the README or a FAQ  
somewhere ...

While I was putzing around with tilecache today, I was never able to  
set metaTile=yes even when  I got it working for single tiles.  I was  
using the MapServerLayer ... I eventually traced it to 24 bit PNG  
output.  PIL was complaining about being unable to read interlaced  
png files.  Fortunately you can turn this off in MapServer by adding  
a FORMATOPTION "INTERLACE=OFF" to your OUTPUTFORMAT block.

Another gotcha ... when seeding (with 1.8.1), if your extents don't  
result in full tiles at your chosen resolutions, some tiles at the  
edges will not get rendered during seeding.  This is only a problem  
if you want to use the TileCache layer to point directly to the  
generated tilecache (which is what I want to do).  Otherwise, it is  
pretty safe to just let the edges get generated when they are needed  
the first time.

When seeding with 1.9 (unreleased at this time), there is an  
undocumented option for the layer configuration in tilecache.cfg, you  
can set 'extent_type=loose' which will cause the edge tiles (that are  
partially outside of the extents) to be generated.

Cheers

Paul


+-----------------------------------------------------------------+
|Paul Spencer                          pspencer at dmsolutions.ca    |
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|Chief Technology Officer                                         |
|DM Solutions Group Inc                http://www.dmsolutions.ca/ |
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