vcglib/vcg/complex/trimesh/inertia.h

/****************************************************************************
* VCGLib                                                            o o     *
* Visual and Computer Graphics Library                            o     o   *
*                                                                _   O  _   *
* Copyright(C) 2005                                                \/)\/    *
* Visual Computing Lab                                            /\/|      *
* ISTI - Italian National Research Council                           |      *
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* This program is distributed in the hope that it will be useful,           *
* but WITHOUT ANY WARRANTY; without even the implied warranty of            *
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* GNU General Public License (http://www.gnu.org/licenses/gpl.txt)          *
* for more details.                                                         *
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History

$Log: not supported by cvs2svn $
Revision 1.3  2006/03/29 10:12:08  corsini
Add cast to avoid warning

Revision 1.2  2005/12/12 12:08:30  cignoni
First working version

Revision 1.1  2005/11/21 15:58:12  cignoni
First Release (not working!)


Revision 1.13  2005/11/17 00:42:03  cignoni
****************************************************************************/
#ifndef _VCG_INERTIA_
#define _VCG_INERTIA_

/*
The algorithm is based on a three step reduction of the volume integrals 
to successively simpler integrals. The algorithm is designed to minimize 
the numerical errors that can result from poorly conditioned alignment of 
polyhedral faces. It is also designed for efficiency. All required volume 
integrals of a polyhedron are computed together during a single walk over 
the boundary of the polyhedron; exploiting common subexpressions reduces 
floating point operations.

For more information, check out:

Brian Mirtich, 
``Fast and Accurate Computation of Polyhedral Mass Properties,''
journal of graphics tools, volume 1, number 2, 1996

*/

#include <vcg/math/matrix33.h>
#include <vcg/math/lin_algebra.h>

#include <vcg/complex/trimesh/update/normal.h>
namespace vcg
{
  namespace tri
  {
template <class InertiaMeshType>
class Inertia
{
  typedef InertiaMeshType MeshType; 
	typedef typename MeshType::VertexType     VertexType;
	typedef typename MeshType::VertexPointer  VertexPointer;
	typedef typename MeshType::VertexIterator VertexIterator;
	typedef	typename MeshType::ScalarType			ScalarType;
	typedef typename MeshType::FaceType       FaceType;
	typedef typename MeshType::FacePointer    FacePointer;
	typedef typename MeshType::FaceIterator   FaceIterator;
	typedef typename MeshType::ConstFaceIterator   ConstFaceIterator;
	typedef typename MeshType::FaceContainer  FaceContainer;
	typedef typename MeshType::CoordType  CoordType;

private :
	enum {X=0,Y=1,Z=2};
	inline ScalarType SQR(ScalarType &x) const { return x*x;}
	inline ScalarType CUBE(ScalarType &x) const { return x*x*x;}

 int A;   /* alpha */
 int B;   /* beta */
 int C;   /* gamma */

/* projection integrals */
 double P1, Pa, Pb, Paa, Pab, Pbb, Paaa, Paab, Pabb, Pbbb;

/* face integrals */
 double Fa, Fb, Fc, Faa, Fbb, Fcc, Faaa, Fbbb, Fccc, Faab, Fbbc, Fcca;

/* volume integrals */
 double T0, T1[3], T2[3], TP[3];

public:

/* compute various integrations over projection of face */
 void compProjectionIntegrals(FaceType &f)
{
  double a0, a1, da;
  double b0, b1, db;
  double a0_2, a0_3, a0_4, b0_2, b0_3, b0_4;
  double a1_2, a1_3, b1_2, b1_3;
  double C1, Ca, Caa, Caaa, Cb, Cbb, Cbbb;
  double Cab, Kab, Caab, Kaab, Cabb, Kabb;
  int i;

  P1 = Pa = Pb = Paa = Pab = Pbb = Paaa = Paab = Pabb = Pbbb = 0.0;

  for (i = 0; i < 3; i++) {
    a0 = f.V(i)->P()[A];
    b0 = f.V(i)->P()[B];
    a1 = f.V1(i)->P()[A];
    b1 = f.V1(i)->P()[B];
    da = a1 - a0;
    db = b1 - b0;
    a0_2 = a0 * a0; a0_3 = a0_2 * a0; a0_4 = a0_3 * a0;
    b0_2 = b0 * b0; b0_3 = b0_2 * b0; b0_4 = b0_3 * b0;
    a1_2 = a1 * a1; a1_3 = a1_2 * a1; 
    b1_2 = b1 * b1; b1_3 = b1_2 * b1;

    C1 = a1 + a0;
    Ca = a1*C1 + a0_2; Caa = a1*Ca + a0_3; Caaa = a1*Caa + a0_4;
    Cb = b1*(b1 + b0) + b0_2; Cbb = b1*Cb + b0_3; Cbbb = b1*Cbb + b0_4;
    Cab = 3*a1_2 + 2*a1*a0 + a0_2; Kab = a1_2 + 2*a1*a0 + 3*a0_2;
    Caab = a0*Cab + 4*a1_3; Kaab = a1*Kab + 4*a0_3;
    Cabb = 4*b1_3 + 3*b1_2*b0 + 2*b1*b0_2 + b0_3;
    Kabb = b1_3 + 2*b1_2*b0 + 3*b1*b0_2 + 4*b0_3;

    P1 += db*C1;
    Pa += db*Ca;
    Paa += db*Caa;
    Paaa += db*Caaa;
    Pb += da*Cb;
    Pbb += da*Cbb;
    Pbbb += da*Cbbb;
    Pab += db*(b1*Cab + b0*Kab);
    Paab += db*(b1*Caab + b0*Kaab);
    Pabb += da*(a1*Cabb + a0*Kabb);
  }

  P1 /= 2.0;
  Pa /= 6.0;
  Paa /= 12.0;
  Paaa /= 20.0;
  Pb /= -6.0;
  Pbb /= -12.0;
  Pbbb /= -20.0;
  Pab /= 24.0;
  Paab /= 60.0;
  Pabb /= -60.0;
}


void CompFaceIntegrals(FaceType &f)
{
	Point3<ScalarType>  n;
	ScalarType w;
  double k1, k2, k3, k4;

  compProjectionIntegrals(f);

  n = f.N();
  w = -f.V(0)->P()*n;
  k1 = 1 / n[C]; k2 = k1 * k1; k3 = k2 * k1; k4 = k3 * k1;

  Fa = k1 * Pa;
  Fb = k1 * Pb;
  Fc = -k2 * (n[A]*Pa + n[B]*Pb + w*P1);

  Faa = k1 * Paa;
  Fbb = k1 * Pbb;
  Fcc = k3 * (SQR(n[A])*Paa + 2*n[A]*n[B]*Pab + SQR(n[B])*Pbb
	 + w*(2*(n[A]*Pa + n[B]*Pb) + w*P1));

  Faaa = k1 * Paaa;
  Fbbb = k1 * Pbbb;
  Fccc = -k4 * (CUBE(n[A])*Paaa + 3*SQR(n[A])*n[B]*Paab 
	   + 3*n[A]*SQR(n[B])*Pabb + CUBE(n[B])*Pbbb
	   + 3*w*(SQR(n[A])*Paa + 2*n[A]*n[B]*Pab + SQR(n[B])*Pbb)
	   + w*w*(3*(n[A]*Pa + n[B]*Pb) + w*P1));

  Faab = k1 * Paab;
  Fbbc = -k2 * (n[A]*Pabb + n[B]*Pbbb + w*Pbb);
  Fcca = k3 * (SQR(n[A])*Paaa + 2*n[A]*n[B]*Paab + SQR(n[B])*Pabb
	 + w*(2*(n[A]*Paa + n[B]*Pab) + w*Pa));
}


void Compute(MeshType &m)
{
  tri::UpdateNormals<MeshType>::PerFaceNormalized(m);
  double nx, ny, nz;

  T0 = T1[X] = T1[Y] = T1[Z] 
     = T2[X] = T2[Y] = T2[Z] 
     = TP[X] = TP[Y] = TP[Z] = 0;
	FaceIterator fi;
  for (fi=m.face.begin(); fi!=m.face.end();++fi) if(!(*fi).IsD()) {
		FaceType &f=(*fi);
  
    nx = fabs(f.N()[0]);
    ny = fabs(f.N()[1]);
    nz = fabs(f.N()[2]);
    if (nx > ny && nx > nz) C = X;
    else C = (ny > nz) ? Y : Z;
    A = (C + 1) % 3;
    B = (A + 1) % 3;

    CompFaceIntegrals(f);

    T0 += f.N()[X] * ((A == X) ? Fa : ((B == X) ? Fb : Fc));

    T1[A] += f.N()[A] * Faa;
    T1[B] += f.N()[B] * Fbb;
    T1[C] += f.N()[C] * Fcc;
    T2[A] += f.N()[A] * Faaa;
    T2[B] += f.N()[B] * Fbbb;
    T2[C] += f.N()[C] * Fccc;
    TP[A] += f.N()[A] * Faab;
    TP[B] += f.N()[B] * Fbbc;
    TP[C] += f.N()[C] * Fcca;
  }

  T1[X] /= 2; T1[Y] /= 2; T1[Z] /= 2;
  T2[X] /= 3; T2[Y] /= 3; T2[Z] /= 3;
  TP[X] /= 2; TP[Y] /= 2; TP[Z] /= 2;
}

ScalarType Mass()
{ 
	return static_cast<ScalarType>(T0);
}

Point3<ScalarType>  CenterOfMass()
{ 
	Point3<ScalarType>  r;
  r[X] = T1[X] / T0;
  r[Y] = T1[Y] / T0;
  r[Z] = T1[Z] / T0;
	return r;
}
void InertiaTensor(Matrix33<ScalarType> &J ){
	Point3<ScalarType>  r;
  r[X] = T1[X] / T0;
  r[Y] = T1[Y] / T0;
  r[Z] = T1[Z] / T0;
  /* compute inertia tensor */
  J[X][X] = (T2[Y] + T2[Z]);
  J[Y][Y] = (T2[Z] + T2[X]);
  J[Z][Z] = (T2[X] + T2[Y]);
  J[X][Y] = J[Y][X] = - TP[X];
  J[Y][Z] = J[Z][Y] = - TP[Y];
  J[Z][X] = J[X][Z] = - TP[Z];

  J[X][X] -= T0 * (r[Y]*r[Y] + r[Z]*r[Z]);
  J[Y][Y] -= T0 * (r[Z]*r[Z] + r[X]*r[X]);
  J[Z][Z] -= T0 * (r[X]*r[X] + r[Y]*r[Y]);
  J[X][Y] = J[Y][X] += T0 * r[X] * r[Y]; 
  J[Y][Z] = J[Z][Y] += T0 * r[Y] * r[Z]; 
  J[Z][X] = J[X][Z] += T0 * r[Z] * r[X]; 
}

void InertiaTensor(Matrix44<ScalarType> &J )
{
	J.SetIdentity();
	Point3<ScalarType>  r;
  r[X] = T1[X] / T0;
  r[Y] = T1[Y] / T0;
  r[Z] = T1[Z] / T0;
  /* compute inertia tensor */
  J[X][X] = (T2[Y] + T2[Z]);
  J[Y][Y] = (T2[Z] + T2[X]);
  J[Z][Z] = (T2[X] + T2[Y]);
  J[X][Y] = J[Y][X] = - TP[X];
  J[Y][Z] = J[Z][Y] = - TP[Y];
  J[Z][X] = J[X][Z] = - TP[Z];

  J[X][X] -= T0 * (r[Y]*r[Y] + r[Z]*r[Z]);
  J[Y][Y] -= T0 * (r[Z]*r[Z] + r[X]*r[X]);
  J[Z][Z] -= T0 * (r[X]*r[X] + r[Y]*r[Y]);
  J[X][Y] = J[Y][X] += T0 * r[X] * r[Y]; 
  J[Y][Z] = J[Z][Y] += T0 * r[Y] * r[Z]; 
  J[Z][X] = J[X][Z] += T0 * r[Z] * r[X]; 
}


/** Compute eigenvalues and eigenvectors of inertia tensor.
		The eigenvectors make a rotation matrix that aligns the mesh along the axes of min/max inertia
 */
void InertiaTensorEigen(Matrix44<ScalarType> &EV, Point4<ScalarType> &ev )
{
	Matrix44<ScalarType> it;
	InertiaTensor(it);
	Matrix44d EVd,ITd;ITd.Import(it);
	Point4d evd; evd.Import(ev);
	int n;
	Jacobi(ITd,evd,EVd,n);
	EV.Import(EVd);
	ev.Import(evd);
}

/** Compute covariance matrix of a mesh, i.e. the integral
		int_{M} { (x-b)(x-b)^T }dx  where b is the barycenter and x spans over the mesh M
 */
static void Covariance(const MeshType & m, vcg::Point3<ScalarType> & bary, vcg::Matrix33<ScalarType> &C){
	// find the barycenter

	ConstFaceIterator fi;
	ScalarType area = 0.0;
	bary.Zero();
	for(fi = m.face.begin(); fi != m.face.end(); ++fi)
		if(!(*fi).IsD())
			{
				bary += vcg::Barycenter( *fi )* vcg::DoubleArea(*fi);
				area+=vcg::DoubleArea(*fi);
			}
	bary/=area;
	 
	
	C.SetZero();
	// C as covariance of triangle (0,0,0)(1,0,0)(0,1,0)
	vcg::Matrix33<ScalarType> C0;
	C0.SetZero();
	C0[0][0] = C0[1][1] = 2.0;
	C0[0][1] = C0[1][0] = 1.0;
	C0*=1/24.0;

	// integral of (x,y,0) in the same triangle
	CoordType X(1/6.0,1/6.0,0);
	vcg::Matrix33<ScalarType> A, // matrix that bring the vertices to (v1-v0,v2-v0,n)
												At,DC;
	for(fi = m.face.begin(); fi != m.face.end(); ++fi)
		if(!(*fi).IsD())
		{
			const CoordType &P0 = (*fi).P(0);
			const CoordType &P1 = (*fi).P(1);
			const CoordType &P2 = (*fi).P(2);
			CoordType  n = ((P1-P0)^(P2-P0));
			const float da = n.Norm();
			n/=da*da;

			A.SetColumn(0,P1-P0);
			A.SetColumn(1,P2-P0);
			A.SetColumn(2,n);
			CoordType delta = P0 - bary;

			At= A;
			At.Transpose();
			/* DC is calculated as integral of (A*x+delta) * (A*x+delta)^T over the triangle,
				 where delta = v0-bary
			*/

			DC.SetZero();
			DC+= A*C0*At;
			vcg::Matrix33<ScalarType> tmp;
			tmp.OuterProduct(A*X,delta);
			DC+= tmp;
			tmp.Transpose();
			DC+= tmp;
			tmp.OuterProduct(delta,delta);
			DC+=tmp*0.5;
// 		DC*=fabs(A.Determinant());	// the determinant of A is the jacobian of the change of variables A*x+delta
 			DC*=da;											// the determinant of A is also the double area of *fi
			C+=DC;
	}

}
}; // end class Inertia

  } // end namespace tri
} // end namespace vcg


#endif