PostGIS's st_overlaps method is only returning results overlapping the LinearRing which makes up the exterior of the polygon I'm searching under

Question

I'm using PostGIS on ruby/rails, and have created a simple box-like polygon under which I wish to search for land parcels in a county. The st_overlaps tool has worked for this before and it has worked this time, sort of.

So I created the polygon to search for parcels (multi-polygons, as it turns out) underneath it

factory = RGeo::Cartesian.factory
coords = [[1554780, 1101102], [1561921, 1062647], [1634713, 1097531], [1630867, 1140657]]
points = coords.map { |pair| RGeo::WKRep::WKTParser.new.parse("POINT (#{pair.first} #{pair.last})") }
ring = factory.linear_ring(points)
polygon = factory.polygon(ring)

After running the active record call:

Parcel.where{st_overlaps(:parcel_multipolygon, polygon)}

I get 157 results. Far less than expected. I exported them a kml file using a custom script of mine. I will upload it soon for viewing.

What you'll see in that kml once loaded in Google Earth, is a parallelogram of pins marking parcels whose areas (polygons) are clearly saddling the outer ring of the parameter-polygon I created to search under. There are so many parcels along these invisible lines in such a clear, distinct shape, the fact that there are no pins in the middle of the shape clearly indicate that the search results were only at the overlappings of parcel multipolygons with the exterior edges (LinearRing) of the search polygon.

Based on my re-reading of the documentation for st_overlaps, I'm left puzzled as to what seems to be the problem here.

Here's a link to view the kmz export. (coordinates converted to geographic before export). You can view it in your browser. The search-polygon itself is not included, but its easy to see where its exterior ring is https://docs.google.com/file/d/0B5inC0VAuhH1TXdTbWQ2RngxZk0/edit?usp=sharing

Answer 1

I think it is behaving as expected. St_overlaps will give features that actually lie on top of each other. If you want all features inside the polygon try ST_Intersects.