DWithin question (distance defintion in Mapserver)

[Bart van den Eijnden]

Hi list,

in my application I am trying to look up which polygon contains a certain point. Since Mapserver WFS does not support Contains, I currently use DWithin.

How does the DWithin internally work? I now have a situation in which the wrong polygon is picked, which makes me suspect it works with calculating the distance from the polygon's centroid, and not the smallest distance towards one of the polygons borders. What does the OGC spec say about this? If I read the OGC Simple Features for SQL I read a different definition for distance:

Distance(anotherGeometry:Geometry):Double*Returns the shortest distance between any two points in
the two geometries as calculated in the spatial reference system of this Geometry.

Btw, I never got an intersect of a point with a polygon layer to work, which was my first plan to solve this.

Any help appreciated. Thanks in advance.

Best regards,
Bart

Bart van den Eijnden
Syncera IT Solutions
Postbus 270
2600 AG  DELFT

tel.nr.: 015-7512436
email: BEN at Syncera-ITSolutions.nl