Hi Coop,
I'm interested in this as well and am planning to get to it
sometime. Rob Blackwell's blog mentioned that he used EPSG:4326
"Virtual Earth uses a WGS84 Mercator projection, but WMS servers need you to
specify the projection. In this case we've specified a Coordinate Reference
System (CRS) of EPSG:4326 which is a common geographic projection that is
equivalent to WGS84."
I suspect this does not work well at high zoom values. I gather as
well that the veapi.js needs to be modified.
Chris Holmes mentions this in his GeoServer 1.5.3 announcement:
http://blog.geoserver.org/2007/08/14/geoserver-embraces-the-geoweb/
"With a bit of coding from Andrea we're also now shipping with support for
the map projection used by Virtual Earth and Google Maps, thanks to SharpGIS
and Chris Schmidt. So now if you use 900913 as the EPSG code for your WMS
requests our output will be perfectly overlaid on those maps."
900913 is a custom EPSG created specific to Google and VE. You can download
the latest version of GeoServer1.5.3 and look at the
configuration\release\user_projections\epsg.properties
900913=PROJCS["WGS84 / Simple Mercator", GEOGCS["WGS 84", DATUM["WGS_1984",
SPHEROID["WGS_1984", 6378137.0, 298.257223563]], PRIMEM["Greenwich", 0.0],
UNIT["degree", 0.017453292519943295], AXIS["Longitude", EAST],
AXIS["Latitude", NORTH]], PROJECTION["Mercator_1SP_Google"],
PARAMETER["latitude_of_origin", 0.0], PARAMETER["central_meridian", 0.0],
PARAMETER["scale_factor", 1.0], PARAMETER["false_easting", 0.0],
PARAMETER["false_northing", 0.0], UNIT["m", 1.0], AXIS["x", EAST], AXIS["y",
NORTH], AUTHORITY["EPSG","900913"]]
You can use the GeoTools projection code by adding this to the EPSG
database. Or you could more simply add your own Java projection code using
the parameters above. http://mathworld.wolfram.com/MercatorProjection.html
Let us know if you succeed in getting the VE WMS overlay working
Thanks
Randy
-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of Brad
Cooper
Sent: Tuesday, August 21, 2007 7:01 AM
To: Geotools-gt2-users@lists.sourceforge.net
Subject: [Geotools-gt2-users] Virtual Earth Transformation Question
Hello all,
I'm new to the GeoTools community and to GIS. I've
searched the archives and couldn't find any
posts/examples on handling Virtual Earth Tile requests
(like this one
http://viavirtualearth.com/vve/Articles/WMS.ashx).
Basically I'd like to create a java based proxy
Servlet that would 1) convert the VE QUAD tile
requests to bounding box coordinates, 2) transform
those coordinates to the appropriate ESPG VE reference
system, 3) send the appropriate request based on the
transformed coordinates to a GeoServer WMS, 4) Stream
the WMS results back to the VE map control.
I understand everything except the transform part.
Does the community have any sample code to transform
the Virtual Earth used WGS84 datum to what I guess
would be some "Mercator projection using a datum based
on WGS84, BUT modified to be spheric"?
Thanks in advance!
Coop
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