Display DOQ at max resolution

[Ed McNierney]

Sean -

Are you requesting the images in UTM projection, or in "geographic" projection?  It doesn't make sense to think about the "geographic" projection as being "1-meter" resolution, since the image has been warped and distorted from the original UTM into a different projection.  The image quality will degrade when that is done, and the pixels in the new image are NOT a "square" number of meters high and wide.  Their width and height are the same number of *degrees*, one of longitude and one of latitude.

All of Microsoft's TerraServer DOQs are JPEG-compressed to begin with, so some data loss is inevitable.  But you should be able to get good image quality when requesting 1-meter resolution in a UTM projection.

     - Ed

Ed McNierney
TopoZone.com

----- Original Message -----
From: Sean Kelly <mapserver at SEAN-KELLY.COM>
To: MAPSERVER-USERS at LISTS.UMN.EDU
Sent: Sun, 10 Oct 2004 14:58:11 -0400
Subject: [UMN_MAPSERVER-USERS] Display DOQ at max resolution


> Hi all,
> 
> I'm working on a setup where the initial display is a WMS layer. (DOQ from
> TerraServer.)
> 
> With the help of Google and the online examples I have been able to hack
> together a setup with php and mapscript where I can display a DOQ from
> TerraServer as a raster layer.  The image is centered on a given lat/long.
> Panning and zooming (out) will be allowed from this starting point. (map
> projection is in latlong and map units are in decimal degrees).
> 
> My problem is I don't seem to be able to calculate extents from my center
> point that allow me to get all the way in to the 1 meter per pixel
> resolution that should be available in the TerraServer image.  I can get
> close, bu I seem to either fall a little short of the desired resolution
> or end up too far in and beyond the scale at which MapServer can render
> the image.  I currently have minscale in the WMS layer set to a very low
> level so it will not interfere with my testing.
> 
> I guess my questions are:
> 
> I'm computing my extents using estimations of lat/long offsets from center
> that will get me "in the ball park" for the resolution I want. Have I
> missed some facility in mapscript that will calculate extents based upon a
> desired center point and scale?
> 
> How might I properly calculate the extents based upon a center point such
> that I can take advantage of the maximum resolution available from the DOQ
> in the raster layer without exceeding the display limits?
> 
> Thanks for any help in advance.
> 
> Sean
>