[postgis-users] DE-9IM question

[Martin Davis]

Have a look at:

http://www.vividsolutions.com/jts/tests/index.html

This is a visual interface to the JTS Test Suite, which has a very 
complete collection of DE-9IM cases.  It is meant to be exhaustive - if 
you find something missing, send it in!  It would be interesting to see 
the 7 situations that you found.

The test suite is here:

http://jts-topo-suite.svn.sourceforge.net/viewvc/jts-topo-suite/trunk/jts/testxml/

The validate directory contains the DE-9IM tests.

As was mentioned, you can use the JTS TestBuilder to build and inspect 
test  cases.  You can drag-and-drop Test Suite XML files onto the 
TestBuilder, so it's easy to inspect the cases in the XML tests.

I'm not sure if Wikipedia would appreciate being flooded with DE-9IM 
test cases - it doesn't seem like quite the right place for it.  The 
Vivid site is a good reference as long as it stays up.

On 5/8/2012 8:46 AM, fork wrote:
> Does anyone know of an exhaustive reference of DE-9IM matrices, with pictures?
>
> Context:
>
> I just finished classifying a bunch of polygons based on their relationship to
> enveloping poly's in another layer (census blocks and census city boundaries,
> respectively).  The regular old st_within() and friends weren't enough, so I
> calculated all the DE-9IM's, counted them (yay for GROUP BY and real
> databases!), and made sure I knew what was going on for each of the matrices
> returned (7 total).  Then I classified my block polys based on the strings.
>
> 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.  Besides the seven in my data,
> there are at least four more that can be generated by various combinations of
> overlapping polygons.
>
> It would have been much easier to do this project if I had been able to
> reference a list of possibilities along with pictures.  It would be even better
> if I could be confident that such a list was exhaustive.
>
> Does anyone have a reference?
>
> If not, I could continue to work on an atlas of DE-9IM matrices, at least for
> polygons, and submit it somewhere if it were helpful.  Any ideas for where that
> might go? (I don't have a blog and don't want to start one).  Maybe just the
> wikipedia entry?
>
> For those who don't know, a DE-9IM matrix is the output of st_relate(geo1,
> geo2), and there is an excellent intro in the docs.  Fascinating stuff really.
>
> Tx
>
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