[Mapserver-users] WMS BBOX vs. Actual Bounds

[Steve Lime]

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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.

Steve

Stephen Lime
Data & Applications Manager

Minnesota DNR
500 Lafayette Road
St. Paul, MN 55155
651-297-2937

>>> John Gorkos <jgorkos at lenexa.sema.slb.com> 1/7/2004 12:20:20 PM >>>
Howdy-
  My programming team is up against a hard deadline, and we're
stymied.
Basic project is this:  use a WMS mapserver to feed a java applet a
base map, 
and then connect (via TCP) to a real-time management system that feeds
us 
status of devices across the planet, coded by lat/long and a status
code.  
These then get overlayed on top of the base map on a "glass pane" that
can be 
changed without redrawing the base.  The result is little winkin',
blinkin' 
lights on top of a map that show (in our case) whether or not
electricity is 
on in various places across the US.
  The problem is that when we send a BBOX request to the mapserver from
the 
java applet, we don't get back a map with the exact coordinates we
asked for.  
That's OK, I realize that mapserver gets as close as it can given the
image 
size, but I've GOT to know what the real boundaries are so I can
overlay my 
status dots on top.  How do I get this information back from the
mapserver?
  On a related thread, how does the mapserver decide what the real
boundaries 
are, when given when the bounds requested don't match the aspect ratio
of the 
returned image?
-- 
John Gorkos
SchlumbergerSema/Atos-Origin
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