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

[Mateusz Loskot]

On 12/09/10 18:14, Greg Troxel wrote:
> 
> Mateusz Loskot <mateusz at loskot.net> writes:
> 
>> -------- Original Message --------
>> Subject: [OSGeo-Standards] Irregular tile coverage in TMS?
>> Date: Sat, 11 Sep 2010 19:46:51 +0200
>> From: Mateusz Loskot <mateusz at loskot.net>
>> To: standards at lists.osgeo.org
>>
>> Folks,
>>
>> I'm reading the TMS spec which says:
>>
>> "a coverage of regularly sized and spaced images that taken together
>> form a complete visual representation of the entire area of coverage"
>>
>> 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?
> 
>> http://www.flickr.com/photos/mloskot/4982635693/
> 
> I'm assuming your TMS would return an error for tiles not in the area
> being covered.  I don't read the spec to prohibit the area not being a
> rectangle.

I have similar impression about the spec.
However, ...

> Practically, it seems clients have to deal with missing tiles anyway.

I'd expect spec to suggest most practical solution in fact.
So, from certain point of view, the TMS spec feels incomplete.

> I don't think your example is prohibited by the specification, and one
> immediately ends up talking about whether the set of available tiles
> would be viewed as useful/reasonable by a tile consumer - which is more
> or less a separate issue.

Perhaps, but considering the spec as a guidance for implementors,
why to allow impractical solutions.

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