Hello to all, I'm developing some spatial queries and have these questions:
1) When one makes an Explain Select request, is there any consideration given to the computational efficiencies of the Postgis functions themselves composing the query? I doubt it, but want to make sure. I assume selection and optimization of the Postgis query functions is independent of the db query design. 2) I have a polygon defined by a hundred points an external point, and wish to calculate an approximate point on the polygon closest to the external point. Assuming the error is acceptable, is it more computationally efficient to calculate on the bounding box than the polygon itself? a) papprox = ST_closestpoint( thegeom(polygon), p_ext) or b) papprox = ST_closestpoint(box2d(thegeom(polygon), p_ext) ?? 3) I have a table of geometries and wish to make combinatorial queries like: SELECT(a.thegeom, b.thegeom, c.thegeom, etc.. WHERE a.thegeom and b.thegeom touch fixed points y and z and c.thegeom intersects geometries a and b. Which is a better approach: a) build temporary tables for a and b geoms, then find c geoms that intersect the entries in the temporary tables or b) perform one select and interate through all the combinations. The number of combinatorials goes exponential very quickly. If one builds temporary tables, how is the spatial index best transferred from original table to the temporary ones ? Does one have to rebuild the index from scratch. thanks, Tom
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