[mapserver-users] Using nquery/mapxy/TOLERANCE/TOLERANCEUNITS

[Steve Lime]

It's possible to use mapxy in conjunction with TOLERANCEUNITS PIXELS but you
have to understand how pixel size is computed for it to work as expected. The 
assumption is that there's a map associated with the point query and it's defined
by a map extent, a width and a height. So, you'd need to define those somehow
too. If not explicitly set as part of a query the defaults in the mapfile are used which
is where things could get convoluted. I can't recall what happens if you define 
mapxy AND mapext with mode=nquery though, which takes precedence in setting
the query method? (looks ambiguous in the code)

Practically speaking, if a query or whatever is associated with a map image regardless
of client environment I *always* use imgxy, imgext and imgsize and populate those
from the client and let MapServer do the conversion. Works fine with the environments 
I use frequently (e.g. OL and dBox). This site does it extensively via OL:

  http://www.dnr.state.mn.us/waters/csg/index_beta.html

Steve

>>> Brent Fraser <bfraser at geoanalytic.com> 10/01/09 10:51 AM >>>
   I'd like someone to confirm my understanding of using 
nquery/mapxy/TOLERANCE/TOLERANCEUNITS.

   GeoMoose v1.6 sets mapxy and imgext (along with mode=nquery and imgsize) CGI 
variables when doing an "Identify Feature" operation.  I'd like to use 
TOLERANCEUNITS PIXELS (and TOLERANCE 3) for my point layer because I think it's 
more intuitive over a range of scales (as opposed to TOLERANCEUNITS METERS, 
TOLERANCE 500).

   This is not possible as using Mapserver's mapxy requires the map file to have 
TOLERANCEUNITS METERS to work properly.  If I want to use TOLERANCEUNITS PIXELS, 
I must use imgxy instead of mapxy because mapserver does not do the conversion 
from mapxy mapping coords to imgxy image coords.

Is this correct?

Thanks!
Brent Fraser
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