[OpenLayers-Users] MapServer, OpenStreetMap, OpenLayers + Reprojection from Latlong to Mercator: a real nightmare

[Mulone]

(apologies for cross-posting)

Hi everybody,

I'm trying to render openstreetmap data on a WMS on MapServer and I posted
something already about this. Now it's time to summarise everything and make
some sense of this.

The system used to work with epsg:4326 (LATLONG from now on) but in our
project we need a GoogleMaps like projection and we chose
epsg:900913/epsg:3785 (MERC from now on).

This is our problem. We need the image on the right but we're getting the
one on the left, a flattened map: 
http://img7.imageshack.us/img7/8279/imagelw.png

After a lot of work and unsucceful tests I post here the outcome, hoping
that it will be helpful to the community - and to us :-)

These are the steps I followed from the very start:

1) download osm xml file from Cloudmade (e.g. Italy.osm.bz2)
2) Run 900913.sql on my PostGIS (optional, it shouldn't matter).
3) import that file into PostGIS with command (latlong option selected):

./osm2pgsql -U userid -W -H host -d maps -p myprefix -S default.style -c -l
italy.osm.bz2

4) At this point everything seems ok. The geometry columns have latlong as
SRID and the tables contain geometries.
It's possible to visualise this dataset with uDig or other tools and
reproject it.

5) Now we want to render this stuff on MapServer. So we add the espg configs
from
 http://spatialreference.org/ref/epsg/3785/ to our mapserver espg file:

<900913> +proj=merc +lon_0=0 +k=1 +x_0=0 +y_0=0 +a=6378137 +b=6378137
+towgs84=0,0,0,0,0,0,0 +units=m +no_defs <>
<3785> +proj=merc +lon_0=0 +k=1 +x_0=0 +y_0=0 +a=6378137 +b=6378137
+towgs84=0,0,0,0,0,0,0 +units=m +no_defs <>

6) define a minimal mapfile with one layer (containing the buildings).

7) run several tests with different projections and annotate the outcome.

Have a look at the report: 
http://docs.google.com/View?id=dftx6j46_166d6r38pcs

Does anybody have any idea about how we could tackle this issue?
I don't know if the problem is arising from MapServer or OpenLayers, so
maybe you can help me design a better test to narrow the problem down.

I presume a lot of people are doing something similar to us, so others might
come across this issue.

Cheers,
Mulone

-----
Mulone
PhD student
-- 
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