[Mapserver-users] WMS BBOX vs. Actual Bounds

[Ed McNierney]

Ian -

I can't agree that this is poor behavior.  MapServer should also be
expected to return a map in the PROJECTION requested, which is
impossible under your scheme.  In WMS mode the SRS is part of the
request and should be respected just as much as the WIDTH, HEIGHT, and
BBOX parameters, shouldn't it?

If you want the image "distorted", you're not looking for a map - you're
making a picture.  If you can define the distortion in a
cartographically accurate way (e.g. a picture), then it is indeed a map;
but you can also provide MapServer with the definition of that
projection and cause it to "distort" the image the way you want.

	- Ed

Ed McNierney
President and Chief Mapmaker
TopoZone.com
ed at topozone.com


-----Original Message-----
From: Ian Turton [mailto:ian at geography.leeds.ac.uk] 
Sent: Thursday, January 08, 2004 5:36 AM
To: Steve Lime; mapserver-users at lists.gis.umn.edu
Subject: Re: [Mapserver-users] WMS BBOX vs. Actual Bounds

At 14:42 07/01/2004 -0600, Steve Lime wrote:
>There's no way with pure WMS (that I know of) to get the computed 
>bounds back other than by precomputing them to perfectly fit your 
>requested image size. I've done that with a java digitizing client that

>took WMS images from MapServer and overlayed information from a 
>seperate SDE/Java application. Worked fine. I've attached the simple 
>map geometry class I used in that case, look at the fit method.
>
>Regarding bounds computation. MapServer gaurantees that the requested 
>extent will fit in the image, so one of the dimensions will remain 
>fixed while the other is expanded as necessary. The decision as to 
>which to expand is based on how the extent is oriented (think portrait 
>vs
>landscape) relative to the "shape" of the image. The idea is to 
>minimize stuff outside the extent.

This is poor behaviour on the part of mapserver - it should return a map
with the bounds requested and the size of image requested, at least when
working in WMS mode.
This saves some heart ache for the client, though in general you want to
request a set of bounds with the same aspect ratio as your image size. 
However, if you actually want the image distorted then mapserver breaks
what you're trying to do.

Ian

Ian Turton, Director, Centre for Computational Geography, University of 
Leeds, Leeds, LS2 9JT
http://www.geog.leeds.ac.uk/people/i.turton http://www.ccg.leeds.ac.uk 
http://www.geotools.org
+44 (0) 113 343 3392 fax: +44 (0) 113 343 3308

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