plane.cpp

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00001 /*
00002  * plane.cpp
00003  *
00004  * Copyright (C) 2010  Thomas A. Vaughan
00005  * All rights reserved.
00006  *
00007  *
00008  * Redistribution and use in source and binary forms, with or without
00009  * modification, are permitted provided that the following conditions are met:
00010  *     * Redistributions of source code must retain the above copyright
00011  *       notice, this list of conditions and the following disclaimer.
00012  *     * Redistributions in binary form must reproduce the above copyright
00013  *       notice, this list of conditions and the following disclaimer in the
00014  *       documentation and/or other materials provided with the distribution.
00015  *     * Neither the name of the <organization> nor the
00016  *       names of its contributors may be used to endorse or promote products
00017  *       derived from this software without specific prior written permission.
00018  *
00019  * THIS SOFTWARE IS PROVIDED BY THOMAS A. VAUGHAN ''AS IS'' AND ANY
00020  * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
00021  * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
00022  * DISCLAIMED. IN NO EVENT SHALL THOMAS A. VAUGHAN BE LIABLE FOR ANY
00023  * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
00024  * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
00025  * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
00026  * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
00027  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
00028  * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
00029  *
00030  *
00031  * Geometry methods specific to 3D planes (2D planes in 3D space)
00032  */
00033 
00034 // includes --------------------------------------------------------------------
00035 #include "plane.h"              // always include our own header first
00036 
00037 
00038 static const float s_eps                = 1.0e-6;
00039 
00040 
00041 ////////////////////////////////////////////////////////////////////////////////
00042 //
00043 //      static helper methods
00044 //
00045 ////////////////////////////////////////////////////////////////////////////////
00046 
00047 
00048 ////////////////////////////////////////////////////////////////////////////////
00049 //
00050 //      public API
00051 //
00052 ////////////////////////////////////////////////////////////////////////////////
00053 
00054 bool
00055 getLineOfIntersection
00056 (
00057 IN const plane_t& A,
00058 IN const plane_t& B,
00059 OUT point3d_t& p0,
00060 OUT point3d_t& pt
00061 )
00062 throw()
00063 {
00064         // intersection line direction is cross product of two plane normals
00065         pt = crossProduct(A.n, B.n);
00066         float n2 = dotProduct(pt, pt);
00067         if (n2 < s_eps) {
00068                 DPRINTF("length of cross product: %f", n2);
00069                 return false;   // cross product is zero--no intersection
00070         }
00071         normalize(pt);
00072 
00073         // now we need to find p0, a point on the intersection line
00074         float ab = dotProduct(A.n, B.n);
00075         float ab2 = ab * ab;
00076         float denom = 1.0 - ab2;
00077         if (denom < s_eps) {
00078                 DPRINTF("1 - ab2 = %f", denom);
00079                 // normals are nearly coincident
00080                 return false;
00081         }
00082 
00083         float b = (B.d - A.d * ab) / denom;
00084         float a = A.d - b * ab;
00085 
00086         p0 = a * A.n + b * B.n;
00087         return true;
00088 }
00089