[mapserver-users] queryByShape returns too many results

[Lime, Steve D (MNIT)]

Pixels probably aren't appropriate in this case. I mean, there isn't an image in play so the pixel cellsize is computed from the default extent and default image size. It can have a profound effect.

If you truly want intersections then set the tolerance to 0 for each layer being queried.

Steve

________________________________
From: Bistrais, Bob [Bob.Bistrais at maine.gov]
Sent: Wednesday, February 20, 2013 4:08 PM
To: Lime, Steve D (MNIT); mapserver-users at lists.osgeo.org
Subject: RE: queryByShape returns too many results

Seems to be line layers.  I reset the tolerance in the map file to 0.1, toleranceunits pixels, but still getting a few records outside of the selection polygon.  I’m confident the projection is OK.  Is there someplace else I should check tolerance?

From: Lime, Steve D (MNIT) [mailto:Steve.Lime at state.mn.us]
Sent: Wednesday, February 20, 2013 4:49 PM
To: Bistrais, Bob; mapserver-users at lists.osgeo.org
Subject: RE: queryByShape returns too many results

It shouldn't matter the shape type. Could it be projection related? Perhaps tolerance related?

Steve

________________________________
From: Bistrais, Bob [Bob.Bistrais at maine.gov]
Sent: Wednesday, February 20, 2013 3:34 PM
To: Lime, Steve D (MNIT); mapserver-users at lists.osgeo.org<mailto:mapserver-users at lists.osgeo.org>
Subject: RE: queryByShape returns too many results
Thanks Steve.

Interestingly, the process you showed me works great with my point data.  But with line or poly data, I am getting some results outside of the polygon.  But, using the nextShape() method works properly with these.

I can but some if/then code in to examine the results based on feature type.  But it would be interesting to know why one way works best for points, the other for lines/polys.

From: Lime, Steve D (MNIT) [mailto:Steve.Lime at state.mn.us]
Sent: Wednesday, February 20, 2013 4:06 PM
To: Bistrais, Bob; mapserver-users at lists.osgeo.org<mailto:mapserver-users at lists.osgeo.org>
Subject: RE: queryByShape returns too many results

You don't use the nextShape() method to retrieve shapes as a result of a query. Here's the pseudo code:

$layer->queryByShape($q_shape);
for($i=0; $i < $layer->getNumResults(); $i++) {
  $shape = $layer->getShape($layer->getResult($i));
  .. do something with the shape ..
}


As part of query operations the bounding box of $q_shape was used to select candidate shapes (that's why nextShape() is returning what is does).

Steve

________________________________
From: mapserver-users-bounces at lists.osgeo.org<mailto:mapserver-users-bounces at lists.osgeo.org> [mapserver-users-bounces at lists.osgeo.org] on behalf of Bistrais, Bob [Bob.Bistrais at maine.gov]
Sent: Wednesday, February 20, 2013 2:38 PM
To: mapserver-users at lists.osgeo.org<mailto:mapserver-users at lists.osgeo.org>
Subject: [mapserver-users] queryByShape returns too many results
I am working on a spatial query module (actually, modifying an existing GeoMoose module) which uses queryByShape to take a previously selected feature from one layer, and use it to select features from another layer.  Both layers are shapefiles, the query layer is of course polygon, the selection layer is points in this case.

When I do the query I am finding too many results are returned- there are many features outside the query polygon which are selected, well beyond the polygon boundary.   The selected features might possibly be within the BBOX of the polygon, but I only want what’s within the polygon.


                $layer->queryByShape($q_shape);
                while($shape = $layer->nextShape()) {
                                # if we have a projection, convert the shape into latlong
                                if($q_shape->intersects($shape) == MS_TRUE or $shape->containsShape($q_shape) == MS_TRUE) {
                                                if($projection != NULL) {
                                                                $shape->project($projection, $LATLONG_PROJ);
                                                }
                                                $foundShapes[] = $shape;
                                }
                }


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