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

[Greg Troxel]

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.

Practically, it seems clients have to deal with missing tiles anyway.
The important property for the set of tiles on the server would seem to
be that given a tile that is not yet at advertised maximum depth one can
get the 4 subtiles.

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.
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