I have done two more trials with generate_image.py and a bit odd results from
both of them.
1. In first case I used PostGIS tables which were projected to epsg:2393. I
gave coordinates for Envelope() in the same units in generate_image.py like
this:
bbox = Envelope(3376400,6672200,3377400,6673200)
PostGIS log shows that same coordinates were used in spatial query
setSRID('BOX3D(3376399.999999945 6672199.999998882,3377399.999999946
6673199.999998933)'::box3d,2393)
However, the rendered image shows only sea and no features from the bounding
box above.
2. In second case I used generate_image.py as it is and changed only database
connection parameters. Database was set to epsg:900913, and I gave the
bounding box as ll, just as adviced in the comments inside generate_image.py.
This system works and generates a nice map. However, if I compare the
coordinates converted from ll to epsg:900913 with cs2cs utility with the
coordinates used in PostGIS queries I can see that they are not the same.
ll bounding box used:
ll (24,60,25,61)
Excerpt taken from the resulting PostGIS query:
'BOX3D(2614284.869242584 8399737.889818355,2840370.179627821
8625823.200203586)'::box3d,900913)
Results of tranforming the bounding box lower left and upper right coordinates
to epsg:9000913 with cs2cs:
C:\ohjelmat\FWTools2.0.6> cs2cs +proj=latlong +datum=WGS84 +to +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]
24 60
2671667.78 8399737.89 0.00
25 61
2782987.27 8625823.20 0.00
So the northing coordinates are the same, but easting coordinates not. As a
result I seem to get much wider map than I was ordering from Mapnik.
In conclusion I have a feeling that there might be something wrong in the way
that generate_image.py is handling projections, at least when used with Windows
version of Mapnik.
-Jukka Rahkonen-
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