[ODE] Pushing through collisions

[Andrew Aye]

    First, it is not always true when the center is pushed deep inside
    cylinder then the side is closer. Imagine when you have a flat
    cylinder with small size but large radius.
    Second,maybe I got the Nan thing you stated before. The depth
    normal is just switch right and left so the small sphere is stuck
    there.


This is slightly confusing.  Even in that example - the axis projection in
the cylindrical axis would have to be larger than the radial direction.  ie.
even if you were intersecting, for example, huge choclate chunks with a big
cookie - it would come up as an axis penetration so long as the distance
from the end of the cylinder to the bottom of the sphere was less than the
distannce from the end of the sphere to the radial limit.  The more likely
occurence with that type of example is that the sphere would tunnel through
the cylinder.  What cylindical collider are you using?

 - Andrew Aye



-----Original Message-----
From: Nguyen Binh [mailto:ngbinh at glassegg.com]
Sent: Friday, April 30, 2004 7:16 AM
To: Alen Ladavac
Cc: ode
Subject: Re[6]: [ODE] Pushing through collisions


Hi Alen,

AL> But, it is the correct solution by definition. Contact normal and depth
AL> define shortest direction and distance along which the two objects need
to
AL> be moved in order not to penetrate.
    Yes!
AL>  If you push sphere deep enough in the
AL> bottom of a cylinder, so that its center is further from the bottom,
than
AL> from the side of the cylinder - then the side is closer, and separation
AL> normal goes that way.
    First, it is not always true when the center is pushed deep inside
    cylinder then the side is closer. Imagine when you have a flat
    cylinder with small size but large radius.
    Second,maybe I got the Nan thing you stated before. The depth
    normal is just switch right and left so the small sphere is stuck
    there.
    
AL>  Generally, if center of one object is inside another
AL> object, you are possibly already in trouble. Though you can calculate
AL> correct resolution for that for primitives, you can't do that for
generic
AL> meshes, so you should avoid such cases in general.
    Hmmm.. I think collider not just need the position and geometric
    information of the two objects, it should consider their
    velocities and or last states,...
    I had used the difference between the flat cylinder and sphere to
    determine what parts of cylinder (side, top, bottom) collided with
    sphere.
    So, I wonder if that's a bad practice? I guess in general mesh
    collider, velocities play some roles...

    
   Nguyen Binh.

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