CGAL曲面网格最短路径演示程序的输入网格变换问题问询

我有一个用于路径规划的网格，正在基于CGAL的Surface_mesh_shortest_path模块开发。使用官方演示程序计算两点间路径时，控制台输出的选中面索引（如5428、4813）及重心坐标为小数值，但我输入的网格顶点坐标数值极大（示例：{334746, 1165, 66225}）。请问该演示程序对输入网格文件执行了何种变换？

#include <CGAL/Exact_predicates_inexact_constructions_kernel.h>
#include <CGAL/Surface_mesh.h>

#include <CGAL/Surface_mesh_shortest_path.h>

#include <CGAL/AABB_face_graph_triangle_primitive.h>
#include <CGAL/AABB_traits.h>
#include <CGAL/AABB_tree.h>

#include <cstdlib>
#include <iostream>
#include <fstream>

typedef CGAL::Exact_predicates_inexact_constructions_kernel             Kernel;
typedef Kernel::Point_3                                                 Point_3;
typedef Kernel::Ray_3                                                   Ray_3;

typedef CGAL::Surface_mesh<Point_3>                                     Triangle_mesh;
typedef CGAL::Surface_mesh_shortest_path_traits<Kernel, Triangle_mesh>  Traits;
typedef CGAL::Surface_mesh_shortest_path<Traits>                        Surface_mesh_shortest_path;

typedef boost::graph_traits<Triangle_mesh>                              Graph_traits;
typedef Graph_traits::vertex_iterator                                   vertex_iterator;
typedef Graph_traits::face_iterator                                     face_iterator;

typedef typename Surface_mesh_shortest_path::Barycentric_coordinates    Barycentric_coordinates;
typedef typename Surface_mesh_shortest_path::Face_location              Face_location;

typedef CGAL::AABB_face_graph_triangle_primitive<Triangle_mesh>         AABB_face_graph_primitive;
typedef CGAL::AABB_traits<Kernel, AABB_face_graph_primitive>            AABB_face_graph_traits;
typedef CGAL::AABB_tree<AABB_face_graph_traits>                         AABB_tree;

typedef CGAL::Surface_mesh<Point_3> Mesh;
typedef Mesh::Vertex_index vertex_descriptor;

int main(int argc, char** argv)
{
  const std::string filename = (argc>1) ? argv[1] : CGAL::data_file_path("meshes/elephant.off");

  Triangle_mesh tmesh;
  if(!CGAL::IO::read_polygon_mesh(filename, tmesh) ||
     !CGAL::is_triangle_mesh(tmesh))
  {
    std::cerr << "Invalid input file." << std::endl;
    return EXIT_FAILURE;
  }

  // or the C++11 for loop. Note that there is a ':' and not a ',' as in BOOST_FOREACH
  for(vertex_descriptor vd : tmesh.vertices()){
    std::cout << tmesh.point(vd) << std::endl;
  }

  Surface_mesh_shortest_path shortest_paths(tmesh);
  const Point_3 source_pt(334746, 1165, 66225);
  Face_location source_loc = shortest_paths.locate<AABB_face_graph_traits>(source_pt); // this builds an AABB tree of the mesh
  shortest_paths.add_source_point(source_loc.first, source_loc.second);
  AABB_tree tree;
  shortest_paths.build_aabb_tree(tree);

  const Point_3 target_pt(370364, 809, 66265.6);
  Face_location target_loc = shortest_paths.locate<AABB_face_graph_traits>(target_pt);

  std::vector<Point_3> points;
  shortest_paths.shortest_path_points_to_source_points(target_loc.first, target_loc.second, std::back_inserter(points));

  // Print the points
  std::cout << points.size() << " ";
  for (std::size_t i = 0; i < points.size(); ++i)
    std::cout << " |----| " << points[i] << "\n";
  std::cout << std::endl;

  return EXIT_SUCCESS;
}

CGAL的Surface_mesh_shortest_path演示程序没有对输入网格的顶点坐标执行任何缩放或变换，你看到的现象是由数据本身的属性决定的：

• 面索引是网格的拓扑属性，仅用于标识网格中的三角面，和顶点坐标的数值大小完全无关，输出的5428、4813就是输入网格中对应面的原始编号。
• 重心坐标是三角面内部的局部坐标表示，用来定位面内的点，其取值范围始终在[0,1]之间（三个坐标之和为1），这是重心坐标的定义特性，和顶点的全局大数值坐标没有关联。
• 从代码逻辑来看，CGAL::IO::read_polygon_mesh仅负责读取网格数据，不会修改原始顶点坐标；locate方法只是通过AABB树查找点所在的面并计算局部重心坐标，也不会对网格做任何变换。

内容的提问来源于stack exchange，提问作者GPrathap