[Mapserver-users] WMS BBOX vs. Actual Bounds

[Kralidis,Tom [Burlington]]

Isn't this the one test which failed for the OGC conformance testing?  IMHO,
we should try to fix this one.

..Tom

> -----Original Message-----
> From: Steve Lime [mailto:steve.lime at dnr.state.mn.us] 
> Sent: Thursday, January 08, 2004 12:04 PM
> To: ian at geography.leeds.ac.uk; 
> mapserver-users at lists.gis.umn.edu; ed at topozone.com
> Subject: RE: [Mapserver-users] WMS BBOX vs. Actual Bounds
> 
> 
> There was a bug filed way back regarding non-square pixels 
> and there has been some progress in supporting this, but it 
> has not been a high priority at all- most folks want square 
> pixels. The work-around I mentioned yesterday is still quite 
> reasonable and works well.
> 
> Steve
> 
> >>> "Ed McNierney" <ed at topozone.com> 1/8/2004 10:46:39 AM >>>
> Ian -
> 
> If you have different scales in X and Y directions, the 
> projection should reflect that.  If the projection is not 
> defined to have different scales, then asking for different 
> scales is not consistent.
> 
> If I ask for a 1,000-meter by 1,000-meter area in UTM 
> projection in an image that's 300 pixels by 200 pixels, it's 
> not possible to do all three.  If I keep the area 1,000x1,000 
> and stretch it to fit in 300x200 pixels, then the projection 
> is no longer UTM.  If I keep the area 1,000x1,000 and the 
> projection UTM, I have to modify the image size and return 
> something square - 300x300, for example.  If I keep the 
> projection UTM and the output image 300x200, then I have to 
> modify the map area to something 1.5:1 - 1,500x1,000 meters, 
> for example. MapServer, of course, chooses the last option, 
> but I have a hard time seeing how any one of the three 
> choices is the "right" answer.
> 
> If you're creating output for a device with non-square 
> pixels, it seems that the way to handle that would be to 
> provide an additional input parameter to the WMS interface, 
> describing the aspect ratio of the the pixels.  This would 
> still allow a client to make an inconsistent request, but it 
> would allow requests intended for non-square pixels to be 
> made consistent with the specified projection.
> 
> However, you are absolutely correct that this is NOT how the 
> WMS specification handles it.  The specification does require 
> the server to stretch the image to fit the box, thereby 
> presuming that any inconsistency in the request is due to a 
> careful client requesting an image for non-square pixels, 
> rather than an error.
> 
> I suppose support for non-rectangular pixels can be left for 
> another discussion <g>.
> 
> 	- 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 10:56 AM
> To: Ed McNierney; mapserver-users at lists.gis.umn.edu 
> Subject: RE: [Mapserver-users] WMS BBOX vs. Actual Bounds
> 
> At 09:20 08/01/2004 -0500, Ed McNierney wrote:
> >Ian -
> >
> >How is it possible to honor all parameters when they are not
> consistent?
> 
> You have different scales in the X and Y directions.
> 
> >I certainly understand the need to deal with unusual output 
> devices as
> 
> >you describe, but it is not very difficult for the client to address
> >that situation.
> 
> It is difficult for the client to deal with if it asks for 
> the image to be distorted but the one it gets back isn't. 
> Mapserver should respect the WMS spec on this point (at least 
> in wms mode).
> 
> 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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