[geos-devel] Robustness of Binary Predicates

[Todd Jellett]

Sorry (again), I should have investigated the crash more closely.

It was not occurring in the touches call but rather because I was trying 
to dynamic_cast a Geometry to a GeometryCollection. The first example I 
sent returned a collection from the intersection call while the second 
(corrected) example correctly returns the intersection as a single 
point. I just wasn't checking the result of the cast.

My real problem is that using a FIXED precision model (scale = 1.0 = 
Whole Numbers) and the LineStrings:
L1 = LINESTRING (-1.0 -2.0, 9.0 5.0, 0.0 0.0, 13.0 6.0)
L2 = LINESTRING (5.0 5.0, 5.0 3.0)

I get:
L2->touches( L1 ) = false
L2->disjoint( L1 ) = true
but
L2->intersection( L1 ) = POINT(5.0 3.0)

How can there be a non-NULL intersection (a single point) but still have 
the 2 geometries *being disjoint and not touching*?

The intersection is correct. I am questioning the correctness of the 
Binary Predicates (touches and disjoint) since both should agree.

Sorry for the confusion
Todd


strk at refractions.net wrote:

>On Wed, Mar 01, 2006 at 12:59:54PM -0400, Todd Jellett wrote:
>  
>
>>Sorry, the second LineString should be:
>>LINESTRING (5.0 5.0, 5.0 3.0)
>>
>>This one crashes in L2->touches( L1 )
>>    
>>
>
>Can you provide an xml test showing the crash ?
>I tried relate(L1,L2) with 2.2.2 and HEAD with
>no crashes.
>
>--strk;
>
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