On Jun 1, 2010, at 12:51 , Joosep-Georg Järvemaa wrote: > 2010/6/1 Andreas Hocevar <[email protected]>: >>>>> >>> 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.
No. Google serves images in Spherical Mercator (EPSG:900913 or EPSG:3857 or whatever EPSG codes there else may exist). maaamet.ee serves images in unprojected WGS84 (EPSG:4326) and EPSG:3301 (a projection suitable for this area). > How hard can be translating coordinates from one EPSG to another? Some > OpenLayers examples show some coordinates-translation being done... It is easy for coordinates. OpenLayers can do it between EPSG:4326 and EPSG:900913, and for other projections you just have to include proj4js. But OpenLayers does not transform map images (which I assume JOSM does). > I > just can not understand how can JOSM have that "computing power" and > browser running on very same machine suddenly does not. JOSM uses the Java VM to do that. And a Java VM, running compiled code, is much faster than a browser, interpreting JavaScript. > My final goal is to start drawing vector data from OSM on that > maaamet.ee WMS layer. Then you will have to include proj4js on your OpenLayers page and transform existing OpenStreetMap data from Spherical Mercator (EPSG:900913 or EPSG:3857 or whatever) to EPSG:3301, and back before you save it. If you also need this aerial imagery, you will have to use EPSG:4326 instead of EPSG:3301, and live with the strange aspect ratio of the displayed map. > 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... You can do it with OpenLayers, but you can only do it with projections that your image server supports. -Andreas. > > > > Regards, > -- > Joosep-Georg > _______________________________________________ > Users mailing list > [email protected] > http://openlayers.org/mailman/listinfo/users -- Andreas Hocevar OpenGeo - http://opengeo.org/ Expert service straight from the developers. _______________________________________________ Users mailing list [email protected] http://openlayers.org/mailman/listinfo/users
