[Tilecache] BBox and MaxExtent

[Chris Whitney]

"Could I specify a maxExtent that aligned with the tilecache grid,  
while still being a subset of the whole?"

	That would be the general idea-- each of the client maxExtents should  
be on the grid.  So, use the max extents and the desired resolution  
from the TileCache configuration to determine the total image size in  
pixels for that zoom level.  Dividing that image size into a 256 pixel  
grid should make it obvious how to calculate the max extent for any  
group of tiles at that zoom level.  (If different clients start at  
different zoom levels, then you have to repeat the process with the  
TileCache max extents and desired resolution.)

-- Chris Whitney


On Jan 23, 2008, at 8:54 AM, Gissur Þórhallsson wrote:

> Hello guys
>
> I’ve got a WMS serving aerial photos of a large area (entire country  
> roughly 100.000 m^2).
> At the moment I’m also tilecaching that entire area.
>
> The problem I’m facing is that I have various openlayer clients  
> running which I intend only to access certain areas (various  
> municipalities and whatnot)
>
> The obvious way to go for me, would be to set a maxExtent on the OL  
> client that encompasses the area that that particular client is  
> allowed to view, while having a Bbox on the tilecache side which  
> encompasses the whole of the country (since some clients DO have  
> access to the whole country).
>
> But when I try this I usually get an error something akin to:
>
> An error occurred: Current x value 352362.838880 is too far from  
> tile corner x 351793.545360
>
> Is there no way to accomplish this? Could I specify a maxExtent that  
> aligned with the tilecache grid, while still being a subset of the  
> whole?
>
> Or am I completely barking up the wrong tree here?
>
> Kind regards,
> Gissur
>
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