include/vamos/geometry/Inertia_Tensor.h

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//      Vamos Automotive Simulator
//  Copyright (C) 2001--2002 Sam Varner
//
//  This program is free software; you can redistribute it and/or modify
//  it under the terms of the GNU General Public License as published by
//  the Free Software Foundation; either version 2 of the License, or
//  (at your option) any later version.
//
//  This program is distributed in the hope that it will be useful,
//  but WITHOUT ANY WARRANTY; without even the implied warranty of
//  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
//  GNU General Public License for more details.
//
//  You should have received a copy of the GNU General Public License
//  along with this program; if not, write to the Free Software
//  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

#ifndef _INERTIA_TENSOR_H_
#define _INERTIA_TENSOR_H_

#include <vamos/geometry/Three_Matrix.h>
#include <vamos/geometry/Three_Vector.h>

namespace Vamos_Geometry
{
  // Exception class thrown if the inertia tensor is singular.
  class Bad_Inertia_Tensor {};

  // Inertia_Tensor describes the inertia tensor for a rigid body.
  class Inertia_Tensor : public Three_Matrix
  {
        // The total mass of all components.
        double m_mass;
        // The inverse of the inertia tensor.
        Three_Matrix m_inverse;

  public:
        // The constructor is trivial.
        
        // Add a mass to the system at `position'.  The inertia tensor
        // components are calculated here.
        void add (double mass, const Three_Vector& position);

        // Zero the components of the inertia tensor and also the mass.
        void zero ();

        // Calculate the inverse of the inertia tensor.  If the tensor is
        // singular, Bad_Inertia_Tensor is thrown.  update() must be
        // called after all add()s have been performed.
        void update ();
        
        // Return the moment of inertia for a force applied at POSITION in
        // the direction FORCE_DIRECTION.  FORCE_DIRECTION need not be a
        // unit vector.
        double inertia (const Three_Vector& position,
                                        const Three_Vector& force_direction) const;

        // Return the moment of inertia for TORQUE applied to the center
        // of mass.  TORQUE need not be a unit vector.
        double inertia (const Three_Vector& torque) const;

        // Return the inverse of the inertia tensor.
        const Three_Matrix& inverse () const { return m_inverse; }
  };
}

#endif

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