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The DE-9IM model isn't designed to be able to distinguish between
these two cases, so there's no way to compute this by using any of
the named predicates, or even a custom relate matrix. <br>
<br>
You could do this via some fairly straightforward custom code. The
algorithm is:<br>
- identify vertices in each linestring which are coincident<br>
- build a simple "local topology" for the 4 incident line segments
at each intersection<br>
- examine the intersection to see if the segments alternate or are
adjacent (you can do this by using the angles of the segments)<br>
<br>
On 5/30/2012 3:40 AM, Jasmin FORMONT wrote:
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<p class="MsoNormal"><span lang="EN-US">Hi everyone<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">I can’t find a way to
tell if two linestrings “really” cross each other.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">For instance if I have
this linestring :<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Line1 : LINESTRING(0 0,
1 1, 2 0)<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">How can I differentiate
the relation of line 1 with one of the following :<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Line2 : LINESTRING(0 2,
1 1, 2 2) -> no “real” cross, just a contact point<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Line3 : LINESTRING(0 2,
1 1, 1 0) -> lines “really” cross each other<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">I can’t find a good
combination of crosses, touches, etc… to differentiate these
cases.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<br>
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