[ODE] Collision detection without forces

[Nguyen Binh]

Hi

gai> Hi,
gai> I'm a newbie with ODE. 
gai> My problem is:

gai> I'm in need to know information (normal,depth....) about the contact points
gai> between two geoms without generating any kind of force.

     In your collision callback function, just dont' create contact
     joint but record those information.

     For example, here is the original code in test_buggy.cpp (ODE 0.5)

static void nearCallback (void *data, dGeomID o1, dGeomID o2)
{
  int i,n;

  // only collide things with the ground
  int g1 = (o1 == ground || o1 == ground_box);
  int g2 = (o2 == ground || o2 == ground_box);
  if (!(g1 ^ g2)) return;

  const int N = 10;
  dContact contact[N];
  n = dCollide (o1,o2,N,&contact[0].geom,sizeof(dContact));
  if (n > 0) {
    for (i=0; i<n; i++) {
      contact[i].surface.mode = dContactSlip1 | dContactSlip2 |
        dContactSoftERP | dContactSoftCFM | dContactApprox1;
      contact[i].surface.mu = dInfinity;
      contact[i].surface.slip1 = 0.1;
      contact[i].surface.slip2 = 0.1;
      contact[i].surface.soft_erp = 0.5;
      contact[i].surface.soft_cfm = 0.3;
      dJointID c = dJointCreateContact (world,contactgroup,&contact[i]);
      dJointAttach (c,
                    dGeomGetBody(contact[i].geom.g1),
                    dGeomGetBody(contact[i].geom.g2));
    }
  }
}

And you could modify to this
static void nearCallback (void *data, dGeomID o1, dGeomID o2)
{
  int i,n;

  // only collide things with the ground
  int g1 = (o1 == ground || o1 == ground_box);
  int g2 = (o2 == ground || o2 == ground_box);
  if (!(g1 ^ g2)) return;

  const int N = 10;
  dContact contact[N];
  n = dCollide (o1,o2,N,&contact[0].geom,sizeof(dContact));
  
  if (n > 0) {
    for (i=0; i<n; i++)
     {
      Save the information (normal,depth....) from contact[i] here....
    }
  }
}


  Hope that helps

-- 
Best regards,

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   Nguyen Binh
   Software Engineer
   Glass Egg Digital Media
   
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