On Thu, Mar 20, 2008 at 10:32 AM, Rahkonen Jukka <[EMAIL PROTECTED]> wrote: > 1. Have I understood right, that in the OSM.XML file, in the layer object, > the actual projection where the data are in database or shapefile, is given? > For example, this layer is originally in spherical mercator, or Google > mercator, or epsg:900913: > <Layer name="power" status="on" srs="+proj=merc +a=6378137 +b=6378137 > +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0 +k=1.0 +units=m [EMAIL PROTECTED] > +no_defs +over">
Correct... > 2. In the same layer object I can either let PostGIS to estimate the > geographical extents of the layer (="estimate_extent">true), or I can give > the extents myself by using the same units that the original data source is > using > <Parameter name="estimate_extent">false</Parameter> > <Parameter > name="extent">-20037508,-19929239,20037508,19929239</Parameter> > Is this right? Or leave out both and the mapnik will always query the layer. estimate_extent doesn't work very well apparently and if you're covering the whole world anyway you're not going to save any useful amount of work by giving an extent. > 3. The output projection of the resulting map is defined in the beginning of > the OSM.XML file > <Map bgcolor="#b5d0d0" srs="+proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 > +lon_0=0.0 +x_0=0.0 +y_0=0 +k=1.0 +units=m [EMAIL PROTECTED] +no_defs +over"> > In this case the output is in spherical marcator, but I should be able to > change it to Finnish KKJ, Zone 3 (epsg:2393) by defining: > <Map bgcolor="#b5d0d0" srs="+proj=tmerc +lat_0=0 +lon_0=27 +k=1.000000 > +x_0=3500000 +y_0=0 +ellps=intl > +towgs84=-90.7,-106.1,-119.2,4.09,0.218,-1.05,1.37 +units=m +no_defs"> > Correct? Correct. > 4. What generate_image.py is actually doing, is > - Tell Mapnik program to take further instructions from environment variable > MAPNIK_MAP_FILE which can be set in Windows with command SET, and if that > does not exist file named osm.xml. > - Pass the size of the resulting image to Mapnik program with imgx and imgy > variables. > - Tell Mapnik to zoom to bounding box that is defined, in the output > projection, with vabiable "bbox" > - And finally render the zoomed box out to image file. > - The projection definition in generate_image.py, as well as prj.forward > stuff in needed because in this script the user is asked to give the extents > of the resulting map in lon-lat bounding box, and this has to be converted > first to "bbox" that is using the units as in the output projection. > Am I still tuned? Looks right... > 5. Finally, if I have defined the srs of the output map to Finnish KKJ in > the osm.xml file as before in number 3, I thought I possibly could give the > extents of the resulting map directly by writing the coordinate array in KKJ > projection inside the bbox = Envelope(). Naturally commenting out some > previous lines where the envelope gets calculated from lon-lat coordinates. > Is my theory correct? Yes, though make sure you get the lat/lon <-> X/Y order correct. > 6. I tried blindly to feed in KKJ coordinates both into Envelope() and also > directly to m.zoom_to_box(bbox) but with no success. All I get back are > error messages telling me that I am feeding in numbers whith are of format > integer, or real or something else, depending on how I wrote the > coordinates, but not as DOUBLE which is the type that some C++ code is only > willing to eat. > Is there some simple way to modify generate_image.py in such a way that I > could get the coordinates I give to passed on as DOUBLE for the Mapnik for > Windows? Can't answer this question without seeing the code you tried to run. Can you paste the changed bits that failed? Have a nice day, -- Martijn van Oosterhout <[EMAIL PROTECTED]> http://svana.org/kleptog/ _______________________________________________ Mapnik-users mailing list [email protected] https://lists.berlios.de/mailman/listinfo/mapnik-users
