RE: [Algorithms] Tris intersection

[Andrew S. <as...@di...>]

You could just use Moller's (excellent) triangle/triangle intersection code
- no point in re-inventing the wheel

- andrew

http://www.ce.chalmers.se/staff/tomasm/code/

> -----Original Message-----
> From: Steve Wood [mailto:Ste...@im...]
> Sent: Sunday, July 23, 2000 9:59 PM
> To: 'gda...@li...'
> Subject: RE: [Algorithms] Tris intersection
> 
> 
> I think the best way to find if the triangles intersect is to 
> take the 3
> vertexes from each triangle one at a time and use it to 
> divide the other
> triangle up into three separate triangles (geometry now not 
> math).  If the
> sum of the area of the three triangles is equal to the area 
> of the whole
> triangle then the triangles intersect (OK, put away your 
> thought compass and
> do the math).  You will need to do this 6 times, 3 times for each
> triangle...  Once you find a vertex where the areas are equal 
> then they
> intersect and you won't have to do the rest of them.
> 
> It's impossible to illustrate with ansii characters so in 
> your mind draw a
> line from point p which represents one of the vertices from the other
> triangle to each vertex a, b, and c to divide the triangle into 3
> triangles...add up the sum of the three triangles, apc, bpa, 
> cpb and compare
> it to the area of abc.  If They are equal then the point is 
> inside, or on
> the triangle (be sure to allow some margin of error for 
> rounding).  Sound
> like a plan?
> 
> a        intersects                    a       does not intersect
> |\                                     |\
> | \                                    | \
> |  \                                   |  \
> |   \                                  |   \
> |    \                                 |    \
> |     \                                |     \
> |      \                               |      \
> |       \                              |       \
> |    .   \                             |        \     .
> |    p    \                            |         \    p
> |          \                           |          \
> |___________\                          |___________\
> c            b                         c            b
> 
> 
> If it solves analytic geometry problems to relax after 10 
> hours of straight
> TFC and Q3A-CTF then it's,
> Rockn-Roll
> 
> 
> > -----Original Message-----
> > From: Jeffrey C [mailto:pl...@as...]
> > Sent: Sunday, July 23, 2000 5:54 PM
> > To: gda...@li...
> > Subject: [Algorithms] Tris intersection
> > 
> > 
> > Hi,
> > 
> > Anyone could tell me a quick way to know whether 2 triangle 
> > that lie on the same plane
> > intersect each other?
> > Let say that I have triangle A(a0,a1,a2) and B(b0,b1,b2), 
> > here is some example that the
> > triangles intersect each other.
> > 
> > |\  /|
> > | / B|
> > | -\--
> > |___\
> >  A
> > 
> >      /|
> >     / |
> >    / B|
> >   /   |
> >  / |\ |
> > /--| \-
> >    |A \
> >    ----
> > 
> > 
> > 
> > 
> > 
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> > 
> 
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