[postgis-users] DE-9IM question

[Martin Davis]

No, we didn't prove exhaustiveness.  But as you can see from the 
documentation in the test cases we did try and formalize a system for 
describing geometric configurations, with the idea that it might lead to 
a way of enumerating all possible distinct situations.  It would be 
interesting to see this pushed through to a proof.

On 5/9/2012 9:32 AM, fork wrote:
> Martin Davis<mtnclimb<at>  telus.net>  writes:
>
>> 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.
> Interesting!  Seems exhaustive to me.  Two comments:  Did you prove
> exhaustiveness - seems like there should be a way to make a combinatorial
> argument about how many possible Clementini matrices are possible (9^4 == 6561,
> less impossible combinations)?  Also - it might be easier to do confirm
> exhaustiveness with simpler shapes, at least for part of the tests.  Still,
> looks great, and comforts me that you are testing that hard.
>
>> 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.
> That is cool!
>
>> 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.
> I will continue to think about this.  I probably don't have time to do fiddle
> with this in any systematic way, but a table with every possible matrix, a
> picture, and simple code to generate it might be pretty useful.
>
>
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