[OSM-dev] Rendering shapefiles under Mercator

Nick Whitelegg nick at hogweed.org
Sat Mar 17 11:19:37 GMT 2007


Hello Artem,

(cc to dev in case anyone else can shed light on this...)

I'm having a bit of trouble rendering shapefiles under Mercator projection. If 
my XML file begins with:

<Map bgcolor="#f2efe9" srs="+proj=merc +datum=WGS84 +k=1.0 +units=m +over
+no_defs">

then I can render the PostGIS database fine, but I am unable to render 
shapefiles containing SRTM height data. The height data *is* in Mercator 
projection (I checked by doing 'shpdump' on the file and get the correct 
coordinates)

On the other hand, if my XML file begins with simply:

<Map bgcolor="#f2efe9">

the Mercator-projected height data actually renders fine - even though I 
haven't specified Mercator. However, the PostGIS won't render.

Is this a known issue or am I doing anything wrong?
The other thing is that rendering the shapefiles is rather slow compared to 
the PostGIS - indeed, prohibitively slow if the shapefile covers a wider area 
than 100km x 100km - would I be better off putting the height data in a 
PostGIS database or using GeoTIFF perhaps? Note that my server only has 160mb 
of ram.

Thanks,
Nick




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