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I have osm.xml file where projection is defined as follows: Map background-color="grey" srs="&srs900913;" minimum-version="2.0.0">

n settings.xml file projection is also set there as:

<!ENTITY osm2pgsql_projection "&srs900913;">

I want to know what is the difference between these 2 projection. I have changed osm2pgsql projection to wgs-84 and it runs f9 for some files. i am confused in this thing


EDIT

When i use srs4326 projection i am getting error on console which is as follow: Unknown projection string, using web mercator as never the less. +init=epsg:4326

I have long/lat coordinates i want to use srs4326 projection

  • First projection is not a projection, but an entity. I guess it denotes EPSG:3857, tile projection. You skipped the second projection definition. For minimizing hassle, I'd recommend installing TileMill and adding your PostGIS layer there: you can specify the projection there with a drop-down box. – Ilja Zverev May 15 '14 at 10:21
  • edited check second one – user2174920 May 15 '14 at 10:30
  • Try changing osm2pgsql_projection to &srs4326; or &srsmercator;. Between those two projections in your question there is obviously no difference. – Ilja Zverev May 15 '14 at 11:44
  • sir both these projections are giving error of unknown projection string – user2174920 May 15 '14 at 11:47
  • See entities.xml.inc for a list of available entities / projections. – Ilja Zverev May 15 '14 at 11:49
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entities.xml.inc lists the possible projections supported by Mapnik:

<!ENTITY srs900913 "+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 +nadgrids=@null +no_defs +over">
<!ENTITY srsmercator "+proj=merc +datum=WGS84 +over">
<!ENTITY srs4326 "+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs +towgs84=0,0,0">

Note that srs900913 is defined on a sphere (EPSG:3857), while srsmercator uses the WGS84 ellipsoid (that's hidden behind +datum=WGS84) usually known as EPSG:3395. Both have a shift of about 20 kilometer unless you are near the aequator. The last one uses lat/lon degree coordinates (EPSG:4326).

Which parameter you have to use depends on the way you stored the data with osm2pgsql. The first one is the default, while the others requires an import with the -M or -l option. But to be honest, I have never seen tiles with those projections, and I am not sure if the style and generate_tile.py files work with that.

In settings.xml.inc you define the entity:

<!ENTITY osm2pgsql_projection "&srs900913;">

which is used inside osm.xml, unless you use the parameter directly:

<Map background-color="#b5d0d0" srs="&srs900913;" minimum-version="2.0.0">
  • thks for reply, i want to use srs4326 as i have long/lat coordinates which i have converted to geometry from st_geomfromtext(). but i am getting an error of unknown projection string – user2174920 May 16 '14 at 4:58
  • You could convert them to EPSG:900913 inside Postgis before rendering. Do you get an error message stating at which module and line the error occured? It would be good to include that in your question. You can still edit it. – AndreJ May 16 '14 at 5:09
  • In your other question, you have srs="&srs900913;" for the Map and srs="&osm2pgsql_projection;" for the layer. This might go wrong if both are not the same. – AndreJ May 16 '14 at 5:14
  • sir you have written in your answer that i have to import with -M or-l option if i have to use srs4326 projection? – user2174920 May 16 '14 at 5:21
  • question edited – user2174920 May 16 '14 at 5:27

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