[ODE] How to perform efficient ray-space collision detection?

[Hampus Soderstrom]

Hi Maciej,

I think you are on the right track. Either you loop through all geoms  
and do dCollide on them with the ray or you use dSpaceCollide with a  
callback. If you think (and measure) that dSpaceCollide is too slow  
you can add collide bits to the geoms to remove unnecesary collisions.

If you go with dSpaceCollide why don't you use the the callback you  
already have instead of a special "ray callback"?

cheers

/Hampa
toribash.com

9 apr 2006 kl. 20.05 skrev Maciej Sawitus:

> Hi everyone,
>
> How would you implement ray-space collision detection?
> I expected there would be
> dCollide(dSpaceID, dGeomID, ...) method
> but there's not.
>
> I can only perform collision detection between 2 geoms.
>
> Below is my (not working) implementation of ray tracing (my cSpace  
> class
> encapsulated ODE's space). In short, I'm creating a "temporary"  
> ray, add
> it to space and now I'd like to intersect it with all other  
> geometries in
> the same space. Unfortunately it doesn't work, because it doesn't  
> compile
> ;) - dCollide can't be given geom and space.
>
> void cSpace::traceRay(const cVec3& start, const cVec3& end,
> cRayTraceResult& result)
> {
>     cVec3 direction = end - start;
>     const Float length = cVec3::length(direction);
>     direction = cVec3::normalize(direction);
>
>     dGeomID rayId = dCreateRay(SpaceId, length);
>     dGeomRaySet(rayId, start[0], start[1], start[2], direction[0],
> direction[1], direction[2]);
>
>     dContact contact;
>     // !!! Doesn't compile !!!
>     const Int numContacts = dCollide(rayId, SpaceId, 1, &contact,
> sizeof(dContact));
>
>     if (numContacts == 0)
>     {
>         result.Hit = false;
>         return;
>     }
>
>     result.Hit = true;
>     result.Depth = contact.geom.depth;
>     result.Normal = contact.geom.normal;
>     result.Position = contact.geom.pos;
>     result.Body = dGeomGetData(contact.geom.g2);
>
>     dGeomDestroy(rayId);
> }
>
> I know I could implement it other way, by adding ray to the space and
> performing regular dSpaceCollide and supplying special "ray  
> callback" to
> it. But it would unnecessarily find all pairs of intersecting  
> geometries
> within my space, while I only want to intersect space with a ray.
>
> I'd be very happy to hear from anyone who implemented ray-space
> intersection.
> Thanks in advance.
>
> Maciej Sawitus
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