AffineXform.cpp

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    1 /**
    2  * MOAB, a Mesh-Oriented datABase, is a software component for creating,
    3  * storing and accessing finite element mesh data.
    4  *
    5  * Copyright 2004 Sandia Corporation.  Under the terms of Contract
    6  * DE-AC04-94AL85000 with Sandia Corporation, the U.S. Government
    7  * retains certain rights in this software.
    8  *
    9  * This library is free software; you can redistribute it and/or
   10  * modify it under the terms of the GNU Lesser General Public
   11  * License as published by the Free Software Foundation; either
   12  * version 2.1 of the License, or (at your option) any later version.
   13  *
   14  */
   15  
   16 /**
   17  * \class AffineXform
   18  * \brief Define an affine transformatino
   19  * \author Jason Kraftcheck (kraftche@cae.wisc.edu)
   20  * \date August, 2006
   21  */
   22  
   23 #ifdef WIN32               /* windows */
   24 #define _USE_MATH_DEFINES  // For M_PI
   25 #endif
   26  
   27 #include "AffineXform.hpp"
   28 #include "moab/Interface.hpp"
   29 #include <cassert>
   30  
   31 namespace moab
   32 {
   33  
   34 // Don't include tag-related stuff in test build because we don't
   35 // link to MOAB to test all other functionality.
   36 const char* const AFFINE_XFORM_TAG_NAME = "AFFINE_TRANSFORM";
   37  
   38 ErrorCode AffineXform::get_tag( Tag& tag_out, Interface* interface, const char* tagname )
   39 {
   40     assert( sizeof( AffineXform ) == 12 * sizeof( double ) );
   41  
   42     if( !tagname ) tagname = AFFINE_XFORM_TAG_NAME;
   43  
   44     return interface->tag_get_handle( tagname, sizeof( AffineXform ), MB_TYPE_DOUBLE, tag_out,
   45                                       MB_TAG_BYTES | MB_TAG_CREAT | MB_TAG_DENSE );
   46 }
   47  
   48 AffineXform AffineXform::rotation( const double* from_vec, const double* to_vec )
   49 {
   50     CartVect from( from_vec );
   51     CartVect to( to_vec );
   52     CartVect a = from * to;
   53     double len = a.length();
   54  
   55     // If input vectors are not parallel (the normal case)
   56     if( len >= std::numeric_limits< double >::epsilon() )
   57     {
   58         from.normalize();
   59         to.normalize();
   60         return rotation( from % to, ( from * to ).length(), a / len );
   61     }
   62  
   63     // Vectors are parallel:
   64     //
   65     // If vectors are in same direction then rotation is identity (no transform)
   66     if( from % to >= 0.0 ) return AffineXform();
   67  
   68     // Parallel vectors in opposite directions:
   69     //
   70     // NOTE:  This case is ill-defined.  There are infinitely
   71     // many rotations that can align the two vectors.  The angle
   72     // of rotation is 180 degrees, but the axis of rotation may
   73     // be any unit vector orthogonal to the input vectors.
   74     //
   75     from.normalize();
   76     double lenxy = std::sqrt( from[0] * from[0] + from[1] * from[1] );
   77     CartVect axis( -from[0] * from[2] / lenxy, -from[1] * from[2] / lenxy, lenxy );
   78     return rotation( -1, 0, axis );
   79 }
   80  
   81 }  // namespace moab