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.

/** @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;
}