[Tilecache] Negative zooms

[Yves Moisan]

Hi,

Sorry for the weird title, but that's the image I get of my problem.  We 
have a bunch of overlays that have widely differing bboxes.  To 
accomodate all of them, we therefore have to choose a very large bbox.  
Now, we have image coverage for a very small area in that bbox, 
basically along a tiny NW-SE line across a small sub-bbox.  We've made a 
tileindex for MapServer and put TC in front.  At zoom levels 0-7, we 
have a tremendous amount of white tiles and mini thumbnails for images 
(useless of course) and the question is how to get rid of that.

Trying to set a smaller bbox in tilecache.cfg does not work (unless I 
find a bbox which happens to match the resolution of one of my original 
zoom levels ?).  So I figured maybe setting a smaller maxextent for my 
whole (openlayers) map and allow people to zoom out from zoomlevel 0 
(whence the negative zoom levels) by not having a restricted extent 
would let me have a zoom level 0 closer to the area where we have images 
for (although there will still be a lot of white tiles at small zoom 
levels, but I guess there isn't much we can do).  I would be in negative 
zoom levels then and the question is can TC be configured not to render 
tiles at those zoom levels ?

Pointers appreciated.

Yves