[OSM-dev] WMSC - bachelor thesis

Oliver Tonnhofer olt at omniscale.de
Thu Aug 18 07:04:24 BST 2011

On 18.08.2011, at 00:26, sorel johann wrote:
>> You will find all that information in the capabilities. See: http://osm.omniscale.net/proxy/tms/1.0.0/osm/EPSG900913
> Do all TMS, mapnik or others provide this capabilities document ? same xml schema ?

That's what the standard specifies and I know that MapProxy, GeoWebCache and TileCache do provide this.

>> That's not completely true. It only describes the top left coordinate and scale denominator. The client needs to know if the projection is in meter, feet or degrees to convert the scale to resolution, so that it can calculate the lower right corner. Don't know what they where thinking…
> WMTS gives you the projection code. so you know what are the projection axis and units.
> If your library can't provide those informations, you should change, handeling projections
> is the De-Facto thing that makes a GIS library, It's just a cartesian library like hundred others if it can't.

Sure, a full blown GIS needs projection handling anyway, but what about web clients? OpenLayers doesn't come with a EPSG database. I don't want to argue that WMTS is more flexible than TMS and that you can do things with it that are not possible with TMS, but in this respect they failed to make simple things easy while making complex things possible.

> beside I don't understand why you need the resolution to find to lower right corner,
> you have the grid size, the size of a tile and the top left corner coordinate, nothing more needed.

Your client needs to know the BBOX of each tiles and you can only calculate that with the resolution.


Oliver Tonnhofer    | Omniscale GmbH & Co KG    | http://omniscale.de
http://mapproxy.org | https://bitbucket.org/olt | @oltonn

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