[OpenLayers-Users] WMS and Mercator projection

[Joosep-Georg Järvemaa]

2010/6/1 Andreas Hocevar <ahocevar at opengeo.org>:
>>>>
>> So you're saying that this JOSM-like behaviour where I have the
>> display picture in EPSG:3857 and am working with real coordinates is
>> not possible at all with OpenLayers?
>
> Exactly. This is why I showed you the other approach - requesting the tiles in the appropriate projection.
>
> In general, reprojecting images on the client needs processing power. Browsers don't have a lot of that.

Well, it's just beyond my understanding how can JOSM do that and why
can OpenLayers not -- only thing what has to be done is ask the image
from the WMS server -- and the server already serves the image in
right projection what I want to see.

The link I'm dragging along is not constructed by myself but is a real
working URI grabbed from JOSM debug output --
http://xgis.maaamet.ee/wms-pub/alus-geo?STYLES=&SRS=EPSG:4326&FORMAT=image/png&VERSION=1.1.1&REQUEST=GetMap&LAYERS=of10000,TOPOYKSUS_6569,TOPOYKSUS_7793&bbox=24.6461274,59.3624859,24.6479219,59.3634004&width=499&height=499

And looking at all those Mercator-examples for OpenLayers something
tells me that it must be possible... Google serves images in Mercator,
right? So does the server at maaamet.ee -- you just have to ask for
the image with EPSG:4326 and real coordinates.

How hard can be translating coordinates from one EPSG to another? Some
OpenLayers examples show some coordinates-translation being done... I
just can not understand how can JOSM have that "computing power" and
browser running on very same machine suddenly does not.


My final goal is to start drawing vector data from OSM on that
maaamet.ee WMS layer.

I just would like to accomplish that without starting to write my own
JavaScript library which would do that because I am not familiar with
GIS internals that much...



Regards,
-- 
Joosep-Georg