A really weird problem with querying a map

Fawcett, David David.Fawcett at STATE.MN.US
Wed Oct 31 16:44:05 EDT 2007

I am not offering this up as complete solution to your problem, although
it would be cool if it was a viable work around.  

I think that this behavior is new in 5.0, but I could be wrong.  I was
thinking that if adding a tolerance to your query changed the result, it
would help us tease out enough symptoms to get a viable bug report.

It would be interesting to run a test to see if this occurs on a layer
where the layer and output are the same SRS.  (e.g. pre-project your


-----Original Message-----
From: UMN MapServer Users List [mailto:MAPSERVER-USERS at LISTS.UMN.EDU] On
Behalf Of Gregor Mosheh
Sent: Wednesday, October 31, 2007 2:37 PM
Subject: Re: [UMN_MAPSERVER-USERS] A really weird problem with querying
a map

Fawcett, David wrote:
> I ran into something with 5.0 and didn't think that much of it.  If 
> you haven't defined a TOLERANCE and TOLERANCEUNITS.  Try a tolerance 
> of 1 meter or something like that.

Well, this is something...

Of note: The data layers are in geographic with NAD27 (EPSG:4269), 
whereas the map's output projection is UTM zone 9 NAD 27 (EPSG:26709). 
Evidently this is very relevant when it comes to queries.

I set these:
and it works well enough to do the job.
But not well enough for me to understand what's happening.

I do find this odd. The documentation says that the defaults for polygon

layers are "0 pixels" meaning that one must click inside the polygon. 
This would be just perfect, but instead I get "nothing found" if I leave

it at that default.

I find it odd that I should have to use such a huge tolerance, too. If I

reduce the tolerance, I start getting all sorts of false positives: 
clicking too close to a border will bring up the neighbor's info. I find

that confusing: I'd think that to be a side effect of a *higher* 
tolerance being set, yes?

Gregor Mosheh / Greg Allensworth
System Administrator, HostGIS cartographic development & hosting
services http://www.HostGIS.com/

"Remember that no one cares if you can back up,
  only if you can restore." - AMANDA

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