Hi Fernando,
thanks for your code. After a quick look, I have some questions; feel
free to let me know that I didn't read the code right.
1. For poly-poly intersection, you check all edges in poly1 against all
edges in poly2 (Interacton.cpp:95). That scales badly (i.e. O(n^2)) and
will be unusable for more complicated polyhedra; I think that GTS or
similar libraries have somehow optimized this (using spatial search
trees, I think, but I am not familiar with that).
2. The repulsive force of both polyhedra depends on penetration of their
bounding spheres, do I read it right?
(dist=normOf(distance_Edge3d_Edge3d(...)); delta=R1+R2-dist;
if(delta>0){ f=n*(Kn*delta) }). I am wondering how that could give
correct results, especially for complex shapes like the jumping cow you
sent.
3. Concerning integration into yade, how do we detect collisions? As we
use aabb's, for irregular shapes the aabb will contain many other bodies
that will not be in contact; but at every step, their contact will have
to be checked for distance. Would it be possible to break (for instance)
the polyhedron into many faces, compute collisions with single faces
(like we do with Facets now) and then interaction the polyhedra as whole
or something similar? (BTW we really should use grid-based collision
detection, esys does that and they take no more than around 10% at the
collision detection even for very large simulations).
To summarize, for anything except Polyhedron-polyhedron, one's probably
better off using facets that we have already; if dynamic behavior is
needed, clumped facets with some mass-bearing sphere in the middle will
do. I thought you would have some sophisticated algorithms for poly-poly
interactions, but it doesn't seem to be the case.
I did run the examples, but didn't see them as I don't have povray
installed here, sorry.
Cheers, Vaclav
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