[postgis-users] DE-9IM question

[fork]

fork <forkandwait <at> gmail.com> writes:

> I found it CRAZY how many different types of DE-9IM's could be returned, even
> with just polygons and very well aligned boundaries (credit to the US Census
> Bureau's geography division).  Only a few of the matrices in my data were
> actually described in the few docs I could find.  

For a flavor, look at Table 3 here:

http://www.cise.ufl.edu/~mschneid/Research/papers/BS01ER.pdf

Note that these matrices are boolean for the intersection, and there are 32 of
them.  One can tweak them so that the max dimension on the boundaries is either
0 (a point) or 1 (a line) and create more matrices using the full definition of
DE-91M; see #33.

I am mostly just entertaining myself with mathematical patterns, but I think the
topological matrices might be useful in trying to figure out how to simplify
slivers and weird things.

I also think one's intuition about "within" might not stand up to closer
scrutiny via mathematical formalisms like this.  The only way I could figure out
my blocks-in-cities problem was to abandon st_within() etc and go for a list of
specific DE-9IM's based on the data.

If I feel bored/ ambitious I will try to create a useful atlas.  I don't think
one exists...