[postgis-users] DE-9IM question

[fork]

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.