[Mapserver-users] Terra Server WMS

[Ed McNierney]

Erich -

Yes, but be careful.

When you say "spanning two UTM zones", do you mean displaying maps in
each of two different zones, or displaying maps that cross the boundary
between two UTM zones?

Your MAP file (or querystring parameters) will specify the OUTPUT
projection of your map.  The PROJECTION blocks in each layer (including
the WMS layers) specify the INPUT projection of each data layer.
MapServer will automatically reproject the requested output area into
the projection of each source layer and select the appropriate data from
that layer (if any) and reproject it to the output projection.

With Microsoft TerraServer's WMS interface, each UTM zone is served as a
WMS layer in its "native" projection.  So if you want data for two
adjacent zones, you create two WMS layers, each with the appropriate
projection block (the NAD83 UTM EPSG codes are 269xx where the last two
digits are the UTM zone number, with a leading zero if needed, as in
Dylan's example).

HOWEVER, Microsoft TerraServer pads the edge of each UTM zone with
"clouds" - their "no-data" imagery.  Here's an example:

http://terraserver.microsoft.com/image.aspx?Lon=-72&Lat=43&w=1&ref=G|-72
,43

This shows a spot at the edge of UTM Zones 18/19.  The projection is UTM
Zone 18, and the area to the east of the zone boundary is "clouds".  If
you use Microsoft TerraServer's imagery this way, you should realize
that you will never see an image that correctly straddles a zone
boundary (it's certainly possible - we've done it on TopoZone for years)
and that any image that crosses the zone edge will look like this.  If
you moved a little east you'd see imagery on the right and clouds on the
left.

Part of the problem is that the TerraServer WMS service reports this
area as "data" and therefore serves an image to you, even though there's
no real imagery there.  The WMS interface doesn't seem to add the
"clouds" but simply returns a solid white area where there's no data.

If it fits your application, you might try using the OFFSITE statement
to make the color white transparent in the WMS layers.  This would then
allow the layer "underneath" to show through.  You would need to make
your map background white, or add a solid white layer underneath the WMS
images, in order to allow the REAL white on the images to be displayed.

	- Ed

Ed McNierney
President and Chief Mapmaker
TopoZone.com / Maps a la carte, Inc.
73 Princeton Street, Suite 305
North Chelmsford, MA  01863
Phone: (978) 251-4242  Fax: (978) 251-1396
ed at topozone.com


-----Original Message-----
From: Erich Schroeder [mailto:erich at museum.state.il.us] 
Sent: Tuesday, June 17, 2003 11:38 AM
To: Dylan Keon
Cc: mapserver-users at lists.gis.umn.edu
Subject: Re: [Mapserver-users] Terra Server WMS

On Tue, 17 Jun 2003, Dylan Keon wrote:

>    PROJECTION
>      "init=epsg:26910" #NAD83 UTM zone 10N
>    END

This is great! I'll be saving this message for future use!

In my case, I would be spanning two utm zones. How would I handle this?
Should there be two doq layers, one for each zone, and then the html
form
turns both on when the user asks for DOQs?

Erich

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Erich Schroeder                    Phone: (217)785-0033
Curator, Information Technologies  FAX:   (217)785-2857
Illinois State Museum GIS Lab      email:erich(at)illinois.state.museum
                 http://illinois.state.museum/
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