ObbTree.cpp

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/** @example ObbTree.cpp
 * This example demonstrates oriented bounding box (OBB) tree construction and ray tracing.
 * It shows how to load a triangular mesh, build an oriented bounding box tree for spatial queries,
 * and perform ray tracing through the mesh to calculate intersection distances and facets.
 * The OBB tree provides efficient spatial partitioning for ray tracing and collision detection applications.
 */
// simple example construct obb tree and ray-tracing the tree
// it reads triangle mesh, construct obb tree and get intersection distances
 
#include "moab/Core.hpp"
#include "moab/Range.hpp"
#include "moab/OrientedBoxTreeTool.hpp"
#include <iostream>
#include <cmath>
 
int main( int argc, char** argv )
{
    if( 1 == argc )
    {
        std::cout << "Usage: " << argv[0] << " <filename>" << std::endl;
        return 0;
    }
 
    // instantiate & load a mesh from a file
    moab::Core* mb = new moab::Core();
    MB_CHK_SET_ERR( mb->load_mesh( argv[1] ), "Couldn't load mesh" );
 
    // get all triangles
    moab::EntityHandle tree_root;
    moab::Range tris;
    // moab::OrientedBoxTreeTool::Settings settings;
 
    MB_CHK_SET_ERR( mb->get_entities_by_type( 0, moab::MBTRI, tris ), "Couldn't get triangles" );
 
    // build OBB trees for all triangles
    moab::OrientedBoxTreeTool tool( mb );
    // rval = tool.build(tris, tree_root, &settings);
    MB_CHK_SET_ERR( tool.build( tris, tree_root ), "Couldn't build tree" );
 
    // build box
    double box_center[3], box_axis1[3], box_axis2[3], box_axis3[3], pnt_start[3], ray_length;
    MB_CHK_SET_ERR( tool.box( tree_root, box_center, box_axis1, box_axis2, box_axis3 ),
                    "Couldn't get box for tree root set" );
 
    ray_length = 2. * sqrt( box_axis1[0] * box_axis1[0] + box_axis1[1] * box_axis1[1] + box_axis1[2] * box_axis1[2] );
 
    // do ray-tracing from box center side to x direction
    std::vector< double > intersections;
    std::vector< moab::EntityHandle > intersection_facets;
 
    for( int i = 0; i < 3; i++ )
        pnt_start[i] = box_center[i] - box_axis1[i];
 
    if( ray_length > 0 )
    {  // normalize ray direction
        for( int j = 0; j < 3; j++ )
            box_axis1[j] = 2 * box_axis1[j] / ray_length;
    }
    MB_CHK_SET_ERR( tool.ray_intersect_triangles( intersections, intersection_facets, tree_root, 10e-12, pnt_start,
                                                  box_axis1, &ray_length ),
                    "Couldn't perform ray tracing" );
 
    std::cout << "ray start point: " << pnt_start[0] << " " << pnt_start[1] << " " << pnt_start[2] << std::endl;
    std::cout << " ray direction: " << box_axis1[0] << " " << box_axis1[1] << " " << box_axis1[2] << "\n";
    std::cout << "# of intersections : " << intersections.size() << std::endl;
    std::cout << "intersection distances are on";
    for( unsigned int i = 0; i < intersections.size(); i++ )
        std::cout << " " << intersections[i];
    std::cout << " of ray length " << ray_length << std::endl;
 
    delete mb;
 
    return 0;
}