Geometry Boost List: [ggl] "touches" in boost.geometry?

Subject: [ggl] "touches" in boost.geometry?
From: Mateusz Loskot (mateusz)
Date: 2011-10-11 00:47:12

On 09/10/11 21:30, Adam Wulkiewicz wrote:
> Barend Gehrels wrote:
>> Hi Aleksandar,
>>
>> The touches algorithm is planned but not included, also not in the
>> extensions. I once started it and today looked at it, but it is not
>> suitable for inclusion yet. However it is on the list.
>>
>> As far as I know it cannot be done by using existing algorithms.
> 
> 
> Hi Barand,
> 
> Please add to the todo list an algorithm checking if geometries
> intersects but not taking boundries into account (intersects() &&
> !touches()

It's imprecise, though it may be understood as self-contradicting.

touches(A, B) is true if and only if
intersect(interior(A), interior(B)) is empty
and
intersect(boundary(A), boundary(B)) is non-empty

I think in terms of the DE-9IM and I believe it's a good
idea to consider or DE-9IM  as basis of all the geometric
relation predicates. It's a generic technique.

BTW, I think having a boundary function would be useful.
We have decided to replace it with convert [1],
but I don't feel it is 1:1

[1] http://trac.osgeo.org/ggl/wiki/OGC

Best regards,
-- 
Mateusz Loskot, http://mateusz.loskot.net
Charter Member of OSGeo, http://osgeo.org
Member of ACCU, http://accu.org