# [mapserver-users] Point inside or outside polygon???

Ed McNierney ed at topozone.com
Thu Aug 1 10:18:40 EDT 2002

```Jan -

The reason this problem is different from the pure mathematical example is that pixels are NOT points in that they have an area.  That's why it's best to leave the answer as "indeterminate".  If I have two polygons sharing an edge, which pixels are drawn in which polygon will depend upon (among other things) the algorithm used, error term initialization, etc.

- Ed

-----Original Message-----
From: Jan Hartmann [mailto:jhart at frw.uva.nl]
Sent: Thursday, August 01, 2002 9:12 AM
To: mapserver-users at lists.gis.umn.edu
Subject: RE: [mapserver-users] Point inside or outside polygon???

Both or none, I would guess. I should vote for both, unless there is a
reason for a point query to exactly return one polygon.

Jan

-----Original Message-----
From: owner-mapserver-users at lists.gis.umn.edu
[mailto:owner-mapserver-users at lists.gis.umn.edu]On Behalf Of Norman Vine
Sent: Thursday, August 01, 2002 1:33 PM
To: mapserver-users at lists.gis.umn.edu
Subject: RE: [mapserver-users] Point inside or outside polygon???

Jan Hartmann writes:
>
>Steve Lime wrote:
>>  You can use a point query against the mapinfo data using the normal
>>  query or nquery modes. One thing to be aware of it that MapServer's
>>  point in polygon routine works fine if the point in question is strictly
>>  in/out of the polygon. It's indeterminate if the point is exactly on the
>>  edge.
>
>Why should the result be indeterminate if the point lies on an edge?

Without considering the 'numerical issues' of what it means to be
'exactly on the edge',  If you have neigboring polygons which poly
would the point be in if it was on the edge  :-)

Cheers

Norman

```