[Tiling] Fwd: [OSGeo-Standards] Irregular tile coverage in TMS?

[Mateusz Loskot]

On 12/09/10 19:54, Oliver Tonnhofer wrote:
> On 12.09.2010, at 13:33, Mateusz Loskot wrote:
>> I understand the size and spacing constraints. What I'm missing,
>> however, is what TMS says about "topological" regularity of tiles
>> within a coverage.
>> 
>> I attached basic drawing with two example tile coverages:
>> 
>> a) blue - regular coverage, rectangular
>> 
>> b) red - irregular coverage
>> 
>> Is only blue version kosher for TMS or both versions are valid?
> 
> It should be valid if your grid size at this level is 4x4 and if you
> are returning empty/transparent images for tiles outside of your
> coverage.

Yes, transparent, empty or tiles of some NODATA rasters...

> An optimization would be to return 301/302 and point to an
> empty image with long expire time, but I don't know how redirects are
> supported in non-browser clients.

This is a Web client aspect which is beyond my question.
I'm trying to discuss TMS without considering
on client side.

> You've got the same problem with WMS/WCS where you can only define a
> bounding box in the capabilities. Requests outside of the coverage
> are transparent, or only contain the background color.

This one gives important input to my question, indeed.

Thus, I'd update asking about actual tiles: are those empty/transparent
tiles actually stored/cached by TMS provider?
If they are, then physically stored tiles coverage could be assumed
as always rectangular.

Best regards,
-- 
Mateusz Loskot, http://mateusz.loskot.net
Charter Member of OSGeo, http://osgeo.org