[OSM-talk] Projections

[Robert (Jamie) Munro]

Christopher Schmidt wrote:
> On Fri, Jan 19, 2007 at 03:37:19PM +0000, SteveC wrote:
>> * @ 19/01/07 03:30:15 PM andrew.rowbottom at gmail.com wrote:
>>>> Are you trying to say that there is a standard for tiling in Mercator
>>>> projection written down somewhere, and we are breaking it?
>>> The big issue here is that the program used to display the tiles must
>>> know the projection used if it wants to convert pixel coordinates (or
>>> tile names) to lat/long. The current implementation assumes a
>>> particular conversion that is not the same for all the different sets
>>> of tiles.
>> The current (top two layers) tiles can be dropped in to google maps -
>> it's a pretty compelling reason to stick with it.
> 
> Unless you're using a different definition than I am, I don't think
> that's true... maybe I'm misunderstanding something though. Google, in
> my experience, uses a simple mercator projection, and OSM isn't creating
> tiles that match that...

It is true. Compare:
 http://mt3.google.com/mt?n=404&v=w2.37&x=4066&y=2713&zoom=4
 http://tile.openstreetmap.org/test/13/4066/2713.png

Out of curiosity, here is MS virtual earth:
 http://r2.ortho.tiles.virtualearth.net/tiles/r0313131122012.png?g=45

Here is the nearest tile from the WMS-C layer (assuming this URL get's
through):
http://labs.metacarta.com/wms-c/Basic.py?LAYERS=osm-merc&FORMAT=image/png&SERVICE=WMS&VERSION=1.1.1&REQUEST=GetMap&STYLES=&EXCEPTIONS=application/vnd.ogc.se_inimage&BBOX=-146763.4025,6731344.66,-141871.43375,6736236.62875&WIDTH=256&HEIGHT=256&SRS=epsg:41001

What is your definition?

Robert (Jamie) Munro

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