Question

We have an application that has a database full of polygons (currently stored as points) that a .net app pulls out and checks if they overlap.

I occurred to me that it would be much nicer to convert these point arrays to polygon / polyline objects within the database and use sql to get a bool of weather they overlap or not.

I have seen different methods suggested to do this but non of the examples given were quite in-line with my needs.

I would be very happy to receive input from those kind enough to offer their experience.

Additional:

In response to questions: It is indeed 2D. and yes any crossover of the two is considered true. The polygons have n points and can be concave. The polygons will be saved as 1 per row (after data conversion task) as polygons (i.e. the polygon type .. it might be called something else spatial / geom my memory is not on my side right now)

Answer 1

You can use .STIntersection with .STAsText() to test for overlapping polygons. (I really hate the terminology Microsoft has used (or whoever set the standard terms). “Touching,” in my mind, should be a test for whether or not two geometry/geography shapes overlap at all, not just share a border.)

Anyway….

If @RadiusGeom is a geometry representing a radius from a point, the following will return a list of any two polygons where an intersection (a geometry that represents the area where two geometries overlap) is not empty.

SELECT CT.ID AS CTID, CT.[Geom] AS CensusTractGeom
FROM CensusTracts CT
WHERE CT.[Geom].STIntersection(@RadiusGeom).STAsText() <> 'GEOMETRYCOLLECTION EMPTY'

If your geometry field is spatially indexed, this runs pretty quickly. I ran this on 66,000 US CT records in about 3 seconds. There may be a better way, but since no one else had an answer, this was my attempt at an answer for you. Hope it helps!