AffineXform.cpp

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/**
 * MOAB, a Mesh-Oriented datABase, is a software component for creating,
 * storing and accessing finite element mesh data.
 *
 * Copyright 2004 Sandia Corporation.  Under the terms of Contract
 * DE-AC04-94AL85000 with Sandia Corporation, the U.S. Government
 * retains certain rights in this software.
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 */

/**
 * \class AffineXform
 * \brief Define an affine transformatino
 * \author Jason Kraftcheck (kraftche@cae.wisc.edu)
 * \date August, 2006
 */

#ifdef WIN32               /* windows */
#define _USE_MATH_DEFINES  // For M_PI
#endif

#include "AffineXform.hpp"
#include "moab/Interface.hpp"
#include 

namespace moab
{

// Don't include tag-related stuff in test build because we don't
// link to MOAB to test all other functionality.
const char* const AFFINE_XFORM_TAG_NAME = "AFFINE_TRANSFORM";

ErrorCode AffineXform::get_tag( Tag& tag_out, Interface* interface, const char* tagname )
{
    assert( sizeof( AffineXform ) == 12 * sizeof( double ) );

    if( !tagname ) tagname = AFFINE_XFORM_TAG_NAME;

    return interface->tag_get_handle( tagname, sizeof( AffineXform ), MB_TYPE_DOUBLE, tag_out,
                                      MB_TAG_BYTES | MB_TAG_CREAT | MB_TAG_DENSE );
}

AffineXform AffineXform::rotation( const double* from_vec, const double* to_vec )
{
    CartVect from( from_vec );
    CartVect to( to_vec );
    CartVect a = from * to;
    double len = a.length();

    // If input vectors are not parallel (the normal case)
    if( len >= std::numeric_limits< double >::epsilon() )
    {
        from.normalize();
        to.normalize();
        return rotation( from % to, ( from * to ).length(), a / len );
    }

    // Vectors are parallel:
    //
    // If vectors are in same direction then rotation is identity (no transform)
    if( from % to >= 0.0 ) return AffineXform();

    // Parallel vectors in opposite directions:
    //
    // NOTE:  This case is ill-defined.  There are infinitely
    // many rotations that can align the two vectors.  The angle
    // of rotation is 180 degrees, but the axis of rotation may
    // be any unit vector orthogonal to the input vectors.
    //
    from.normalize();
    double lenxy = std::sqrt( from[0] * from[0] + from[1] * from[1] );
    CartVect axis( -from[0] * from[2] / lenxy, -from[1] * from[2] / lenxy, lenxy );
    return rotation( -1, 0, axis );
}

}  // namespace moab