[gdal-dev] Accuracy of OGRLayer:SetSpatialFilter() API

[kedardeshpande87]

Frank,

Thank you very much for the reply.

I am still really curious about what could be the reason that it returns
multiple features for a single point.
The code for filtering which I have written is like this : 
...
OGRDataSource *ds = OGRSFDriverRegistrar::Open("shapefile_path", FALSE);
OGRLayer *layer = ds->GetLayer(0);
OGRGeometry *g = new OGRPoint(longitude, latitude);
layer->SetSpatialFilter(g);
OGRFeature *feature = NULL;

while((feature = layer->GetNextFeature()) != NULL) {
       // do something with feature ...
}

As per the API doc, it says : "it is guaranteed that all features who's
envelope (as returned by OGRGeometry::getEnvelope()) overlaps the envelope
of the spatial filter will be returned."

I checked the envelope the OGRPoint geometry I have created. This envelope
is also a single point (minX, maxX are same and minY, maxY are same). So,
how is it possible that multiple features overlap on the same point ?  

For the same shapefile, I checked results by using some other libraries as
well. Those libraries return a single zipcode. So I am guessing the
shapefile which I am using does not have overlapping data.

Could it be that the vector math done while calculating the intersection of
filter-geometry and features has some limitations?
Could you please give me some idea about this ?

Thanks,
Kedar

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