[Mapserver-users] (no subject)

[Ed McNierney]

Marc -

Actually, in most cases TerraServer will serve you the unclipped border of the topo map (if you're using the DRG layer) at the edge of the zone, and will return its "fluffy clouds" no-data image for DOQQs.

Part of the problem is that TerraServer will return what appears to be perfectly valid data in these overedge regions where it actually has no data.  It's very hard on your end to distinguish between valid data that isn't really valid and really valid data.  Even if you did mosaic the edges together, you would end up overlaying the TerraServer "overedge" data (fluffy clouds or topo map margins) on top of your real data for the adjacent zone.

It's a bit of a stretch, but the only technique I can think of to handle this problem would be to create your own WMS server using MapServer and have it act as a front-end to TerraServer.  You can create that server as both a WMS client and a WMS server.  You would want one map file per UTM zone - each map file would have two layers, one pulling the TerraServer data, and the other acting as a distinctive "no-data" mask.  The "no-data" area could just be two inline features, each being a lat/lon area outside the UTM zone of interest.  These would overlay the TerraServer imagery and clip it to the UTM zone.  You would still have overedge "no-data" areas, but they now would be easy to handle.

You then create a second application pulling from this first server.  You now can overlap the two zones with an OFFSITE parameter (it's probably easiest to start with a background pixel value of 0 0 0 (black), create black masks, and then use OFFSITE to make black transparent).  Now you can mosaic the zones together (you'll have to reproject one on the fly, of course) without weird artifacts.

We provide a commercial WMS service to serve USGS imagery.  Unlike TerraServer, it's not free.  Unlike TerraServer, it handles UTM zone edges properly.  Contact me off-list if that's interesting.

	- Ed

Ed McNierney
President and Chief Mapmaker
TopoZone.com / Maps a la carte, Inc.
73 Princeton Street, Suite 305
North Chelmsford, MA  01863
ed at topozone.com
(978) 251-4242 

-----Original Message-----
From: Marc Jacquin [mailto:marc.jacquin at geosys-inc.com]
Sent: Wednesday, February 19, 2003 9:18 AM
To: mapserver-users at lists.gis.umn.edu
Subject: [Mapserver-users] (no subject)


Hi,

Sorry for posting a second time, my E-Mail address did not match the
registered address.

We are using the OGC WMS interface of the Terraserver and that works fine
with an enhanced 3.6 version.
The problem occurs when the WMS request overlaps two UTM zones. If the
request is lat/long the Terraserver returns an exception because the 2
points of the bounding box are in 2 different zones, and if the request is
in the one of the 2 UTM projections, the portion of the image in the other
zone is left blank.

I was wondering if there would be a map file trick to be able to mosaic 2
layers.

Marc



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