[Mapserver-dev] msProjectRect for degenerate rectangles?

[Steve Lime]

This really needs Frank's input since he's the resident projection
guru... My thought would be that in the case of a degenerate rectangle
the output should also be a degenerate rectangle and the projection
boils down to projecting a point. 

Steve

>>> "Ed McNierney" <ed at topozone.com> 03/21/03 09:39AM >>>
Actually, the fix is slightly different than that.  It's probably a bit
of overkill, but if dx == 0 and dy == 0 (i.e. both blocks of code are
skipped) then I passed both the minx, miny and maxx, maxy points to
msProjectGrowRect.  They should be exactly the same point, but I always
worry about comparing floating-point numbers to 0.  msProjectGrowRect
will take care of setting both corners of the rectangle.

  //	If both deltas are zero, the rectangle is small but we need to
do something

  if ((dx == 0) && (dy == 0))
  {
	  prj_point.x = rect->minx;
	  prj_point.y = rect->miny;
	  msProjectGrowRect (in, out, &prj_rect, &rect_initialized,
&prj_point, &failure);
	  prj_point.x = rect->maxx;
	  prj_point.y = rect->maxy;
	  msProjectGrowRect (in, out, &prj_rect, &rect_initialized,
&prj_point, &failure);
  }

	- Ed

Ed McNierney
President and Chief Mapmaker
TopoZone.com / Maps a la carte, Inc.
73 Princeton Street, Suite 305
North Chelmsford, MA  01863
ed at topozone.com 
(978) 251-4242 

-----Original Message-----
From: Ed McNierney 
Sent: Thursday, March 20, 2003 2:20 PM
To: mapserver-dev at lists.gis.umn.edu 
Subject: [Mapserver-dev] msProjectRect for degenerate rectangles?


Folks -

Now that I can actually run queries on 3.7, they don't work <g>.  It
appears that doing a simple single-layer point query (i.e. what object
is this point in) for a data layer that's not in the MAP file's native
projection doesn't work.  The query point is used to initialize a
rectangle with no TOLERANCE values, so msQueryByPoint creates a
degenerate rectangle object (minx == maxx, miny == maxy) and passes it
to msProjectRect.  It *appears* that msProjectRect does the wrong thing
- it looks to see if dx (deltax) is greater than 0, and calls
msProjectGrowRect, then looks to see if dy (deltay) is greater than 0
and calls msProjectGrowRect again.

If dx == 0 and dy == 0 then the output rectangle's values are copied
from prj_rect, which was never initialized.  So I get goofy results and
the query doesn't work.

I'm really asking about what msProjectRect should do when passed a
degenerate rectangle.  It seems to me that there's nothing really wrong
with such a rectangle, and it ought to handle it just fine (i.e. the fix
should be in msProjectRect).  But I don't know enough about its usage to
be sure.

It seems like modifying the two tests (if (dx > 0), if (dy > 0)) to
simply be >= tests would be fine.  Thoughts would be appreciated -
thanks.

	- Ed

Ed McNierney
President and Chief Mapmaker
TopoZone.com / Maps a la carte, Inc.
73 Princeton Street, Suite 305
North Chelmsford, MA  01863
ed at topozone.com 
(978) 251-4242 

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