Hi, according to the source code, the legacy option -M is using this projection:
[PROJ_MERC] = {
descr: "WGS84 Mercator",
proj4text: "+proj=merc +datum=WGS84 +k=1.0 +units=m +over +no_defs",
srs:3395,
option: "" }
Unlike EPSG:900913, that projection is not assuming that the Earth is a perfect
sphere, therefore:
- it seems to be cartographically more correct
- it probably needs far more computation
- the result probably differs from that of EPSG:900913 by a few meters
Regards
Juan Lucas
________________________________
De: talk-boun...@openstreetmap.org en nombre de Francois Van
Der Biest
Enviado el: vie 01/05/2009 17:52
Para: talk@openstreetmap.org
Asunto: [OSM-talk] osm2pgsql and proper/legacy mercator
Hi list,
osm2pgsql --help says:
-m|--merc: Store data in proper spherical mercator (default)
-M|--oldmerc: Store data in the legacy OSM mercator format
I'm wondering what's the difference between those two srs.
Which one is epsg:900913 (aka epsg:3785
http://www.spatialreference.org/ref/epsg/3785/) ?
My experience (importing an osm dump into postgis, then
exporting to
shapefiles) would let me think that the "legacy OSM mercator
format"
is epsg:3785. So, what's the other one ?
Thank's,
F.
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