[Tilecache] SRS parameter

[Mauclerc Anthony]

Hello,
 
I'm in charge of a web application (InfoTerre) that shares french
geological information. In the current version, we use MapBuilder 1.0 on
client side to request our WMS servers, with some developments around
that tool. One of those customizations consists in switching the SRS at
runtime with respect to the location and the scale : for instance, the
SRS is Lambert II if you are in France but switches to WGS84 if you zoom
out enough (if I am not clear, I let you see it at
http://infoterre.brgm.fr <http://infoterre.brgm.fr/> ). Of course, the
WMS server has to be able to deal with both projections. 
 
Presently, for performance issues, we are working on a new version that
embeds MapBuilder 1.5 (based on OpenLayers) and that uses some raster
layers as WMS-C (we use TileCache). So far, our tests are promising
since we can get the default raster layer on France in Lambert II.
However, TileCache does not take SRS into account which is blocking for
us. 
 
We are thinking of implementing SRS switching in TileCache (we could
generate independently, let's say, 3 levels in EPSG4326 and 7 levels in
EPSG27582, with potentialy level overlaps and requests the same
TileCache and the same layer in EPSG4326 and EPSG27582). I do not know
much about TileCache code architecture but I imagine we could add a top
level folder in the tile storage that specifies the SRS : 
 
EPSG4326
    Level 01
        Tile001
        Tile002
        ...
    Level 02
        Tile001
        Tile002
        ...
    ...
EPSG27582
    Level 01
        Tile001
        Tile002
        ...
    Level 02
        Tile001
        Tile002
        ...
    ...
 
Does it seem to you reasonable or totaly crazy ? Moreover, would you
have some advice on that hazardeous project ;) ? 
Thank you for any help you could provide. 
 
Regards
 
--
Anthony Mauclerc
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