/// Perform disc-terrain collision detection.
/// This utility function checks for contact between a disc of specified
/// radius with given position and orientation (specified as the location of
/// its center and a unit vector normal to the disc plane) and the terrain
/// system associated with this tire. It returns true if the disc contacts the
/// terrain and false otherwise. If contact occurs, it returns a coordinate
/// system with the Z axis along the contact normal and the X axis along the
/// "rolling" direction, as well as a positive penetration depth (i.e. the
/// height below the terrain of the lowest point on the disc).
protected static bool disc_terrain_contact(
ChTerrain terrain, ///< [in] reference to terrain system
ChVector disc_center, ///< [in] global location of the disc center
ChVector disc_normal, ///< [in] disc normal, expressed in the global frame
double disc_radius, ///< [in] disc radius
ref ChCoordsys contact, ///< [out] contact coordinate system (relative to the global frame)
ref double depth ///< [out] penetration depth (positive if contact occurred)
)
{
// Find terrain height below disc center. There is no contact if the disc
// center is below the terrain or farther away by more than its radius.
double hc = terrain.GetHeight(disc_center.x, disc_center.y);
if (disc_center.z <= hc || disc_center.z >= hc + disc_radius)
{
return(false);
}
// Find the lowest point on the disc. There is no contact if the disc is
// (almost) horizontal.
ChVector nhelp = terrain.GetNormal(disc_center.x, disc_center.y);
ChVector dir1 = ChVector.Vcross(disc_normal, nhelp);
double sinTilt2 = dir1.Length2();
if (sinTilt2 < 1e-3)
{
return(false);
}
// Contact point (lowest point on disc).
ChVector ptD = disc_center + disc_radius * ChVector.Vcross(disc_normal, dir1 / Math.Sqrt(sinTilt2));
// Find terrain height at lowest point. No contact if lowest point is above
// the terrain.
double hp = terrain.GetHeight(ptD.x, ptD.y);
if (ptD.z > hp)
{
return(false);
}
// Approximate the terrain with a plane. Define the projection of the lowest
// point onto this plane as the contact point on the terrain.
ChVector normal = terrain.GetNormal(ptD.x, ptD.y);
ChVector longitudinal = ChVector.Vcross(disc_normal, normal);
longitudinal.Normalize();
ChVector lateral = ChVector.Vcross(normal, longitudinal);
ChMatrix33 <double> rot = new ChMatrix33 <double>(0); // Need to nest this.
rot.Set_A_axis(longitudinal, lateral, normal);
contact.pos = ptD;
contact.rot = rot.Get_A_quaternion();
depth = ChVector.Vdot(new ChVector(0, 0, hp - ptD.z), normal);
//assert(depth > 0);
return(true);
}
/// Given point B and a generic triangle, computes the distance from the triangle plane,
/// returning also the projection of point on the plane and other infos
/// \return the signed distance
public static double PointTriangleDistance(ChVector B, //< point to be measured
ref ChVector A1, //< point of triangle
ref ChVector A2, //< point of triangle
ref ChVector A3, //< point of triangle
ref double mu, //< returns U parametric coord of projection
ref double mv, //< returns V parametric coord of projection
ref bool is_into, //< returns true if projection falls on the triangle
ref ChVector Bprojected //< returns the position of the projected point
)
{
// defaults
is_into = false;
mu = mv = -1;
double mdistance = 10e22;
ChVector Dx, Dy, Dz, T1, T1p;
Dx = ChVector.Vsub(A2, A1);
Dz = ChVector.Vsub(A3, A1);
Dy = ChVector.Vcross(Dz, Dx);
double dylen = ChVector.Vlength(Dy);
if (Mathfx.Abs(dylen) < EPS_TRIDEGENERATE) // degenerate triangle
{
return(mdistance);
}
Dy = ChVector.Vmul(Dy, 1.0 / dylen);
ChMatrix33 <double> mA = new ChMatrix33 <double>(0);
ChMatrix33 <double> mAi = new ChMatrix33 <double>(0);
mA.Set_A_axis(Dx, Dy, Dz);
// invert triangle coordinate matrix -if singular matrix, was degenerate triangle-.
if (Mathfx.Abs(mA.FastInvert(mAi)) < 0.000001)
{
return(mdistance);
}
T1 = mAi.Matr_x_Vect(ChVector.Vsub(B, A1));
T1p = T1;
T1p.y = 0;
mu = T1.x;
mv = T1.z;
if (mu >= 0 && mv >= 0 && mv <= 1.0 - mu)
{
is_into = true;
mdistance = Mathfx.Abs(T1.y);
Bprojected = ChVector.Vadd(A1, mA.Matr_x_Vect(T1p));
}
return(mdistance);
}