[Mapserver-users] Terra Server WMS

[Erich Schroeder]

Thanks Ed, this makes it clear that I'll have to experiment. When I 
develop things, I'll be dealing with Illinois which spans zones 15 & 16. I 
have access to a doq set projected into an extended 15 (if I remember 
right), so I might have to use that. Still, I was liking the idea of using 
Terraserver if that was possible, thereby saving my disk space.

Erich

On Tue, 17 Jun 2003, Ed McNierney wrote:

> 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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