为什么在下列代码中如何表示与*v_it与prev_vh表示的是同一个点：float smoothCot() { float err = -1; cogs.clear(); v_end = mesh.vertices_end(); // for (v_it = mesh.vertices_begin(); v_it != v_end; ++v_it) { cog[0] = cog[1] = cog[2] = valence = 0.0; //cout << valence<<"1" << endl; for (vv_it = mesh.vv_iter(*v_it); vv_it.is_valid(); ++vv_it) { double cot_weight = 0.0; MyMesh::HalfedgeHandle heh = mesh.find_halfedge(*v_it, *vv_it); if (!mesh.is_boundary(heh)) { MyMesh::HalfedgeHandle prev_heh = mesh.prev_halfedge_handle(heh); MyMesh::HalfedgeHandle next_heh = mesh.next_halfedge_handle(heh); MyMesh::VertexHandle prev_vh = mesh.to_vertex_handle(prev_heh); MyMesh::VertexHandle next_vh = mesh.to_vertex_handle(next_heh); MyMesh::Point prev_p = mesh.point(prev_vh); MyMesh::Point curr_pi = mesh.point(*v_it); MyMesh::Point curr_pj = mesh.point(*vv_it); MyMesh::Point next_p = mesh.point(next_vh); double cot_alpha = cot(curr_pi - prev_p, curr_pj - prev_p); double cot_beta = cot(curr_pi - next_p, curr_pj - next_p); cot_weight = cot_alpha + cot_beta; //cout << cot_weight<<"2" << endl; } cog += cot_weight *( mesh.point(*vv_it)-mesh.point(*v_it)); valence += cot_weight; //cout << valence<<"3" << endl; } cogs.push_back(cog / valence); } for (v_it = mesh.vertices_begin(), cog_it = cogs.begin(); v_it != v_end; ++v_it, ++cog_it) { if (!mesh.is_boundary(*v_it)) { MyMesh::Point p = mesh.point(*v_it); //*cog_it += mesh.point(*v_it); err = max(err, (p - *cog_it).norm()); mesh.set_point(*v_it, *cog_it); } } return err; }

在这段代码中，*v_it是当前点的句柄，prev_vh是prev_p所在的点的句柄。如果要表示它们是同一个点，可以使用prev_vh.idx() == v_it->idx()这个条件来判断，因为prev_vh.idx()返回的是prev_vh所在的点的索引，v_it->idx()返回的是当前点的索引，如果它们相等，那么*v_it和prev_vh就表示同一个点。所以可以在代码中添加一个判断条件if (prev_vh.idx() == v_it->idx()) { prev_p = mesh.point(*v_it); }来表示它们是同一个点。

相关问题

为什么在下列代码中如何表示与curr_pi与prev_p表示的是同一个点：float smoothCot() { float err = -1; cogs.clear(); v_end = mesh.vertices_end(); // for (v_it = mesh.vertices_begin(); v_it != v_end; ++v_it) { cog[0] = cog[1] = cog[2] = valence = 0.0; //cout << valence<<"1" << endl; for (vv_it = mesh.vv_iter(*v_it); vv_it.is_valid(); ++vv_it) { double cot_weight = 0.0; MyMesh::HalfedgeHandle heh = mesh.find_halfedge(*v_it, *vv_it); if (!mesh.is_boundary(heh)) { MyMesh::HalfedgeHandle prev_heh = mesh.prev_halfedge_handle(heh); MyMesh::HalfedgeHandle next_heh = mesh.next_halfedge_handle(heh); MyMesh::VertexHandle prev_vh = mesh.to_vertex_handle(prev_heh); MyMesh::VertexHandle next_vh = mesh.to_vertex_handle(next_heh); MyMesh::Point prev_p = mesh.point(prev_vh); MyMesh::Point curr_pi = mesh.point(*v_it); MyMesh::Point curr_pj = mesh.point(*vv_it); MyMesh::Point next_p = mesh.point(next_vh); double cot_alpha = cot(curr_pi - prev_p, curr_pj - prev_p); double cot_beta = cot(curr_pi - next_p, curr_pj - next_p); cot_weight = cot_alpha + cot_beta; //cout << cot_weight<<"2" << endl; } cog += cot_weight *( mesh.point(*vv_it)-mesh.point(*v_it)); valence += cot_weight; //cout << valence<<"3" << endl; } cogs.push_back(cog / valence); } for (v_it = mesh.vertices_begin(), cog_it = cogs.begin(); v_it != v_end; ++v_it, ++cog_it) { if (!mesh.is_boundary(*v_it)) { MyMesh::Point p = mesh.point(*v_it); //*cog_it += mesh.point(*v_it); err = max(err, (p - *cog_it).norm()); mesh.set_point(*v_it, *cog_it); } } return err; }

在这段代码中，curr_pi是当前点的位置，prev_p是它的前一个点的位置。如果要表示它们是同一个点，可以使用prev_vh == *v_it这个条件来判断，因为prev_vh是prev_p所在的点的句柄，*v_it是当前点的句柄，如果它们相等，那么prev_p和curr_pi就表示同一个点。所以可以在代码中添加一个判断条件if (prev_vh == *v_it) { prev_p = mesh.point(*v_it); }来表示它们是同一个点。

将下列代码改为vs内可运行的代码：float smoothCot() { float err = -1; cogs.clear(); v_end = mesh.vertices_end(); // for (v_it = mesh.vertices_begin(); v_it != v_end; ++v_it) { cog[0] = cog[1] = cog[2] = valence = 0.0; for (vv_it = mesh.vv_iter(*v_it); vv_it.is_valid(); ++vv_it) { double cot_weight = 0.0; MyMesh::HalfedgeHandle heh = mesh.find_halfedge(*v_it, *vv_it); if (!mesh.is_boundary(heh)) { MyMesh::HalfedgeHandle prev_heh = mesh.prev_halfedge_handle(heh); MyMesh::HalfedgeHandle next_heh = mesh.next_halfedge_handle(heh); MyMesh::VertexHandle prev_vh = mesh.to_vertex_handle(prev_heh); MyMesh::VertexHandle next_vh = mesh.to_vertex_handle(next_heh); MyMesh::Point prev_p = mesh.point(prev_vh); MyMesh::Point curr_p = mesh.point(*v_it); MyMesh::Point next_p = mesh.point(next_vh); double cot_alpha = cot(prev_p - curr_p, next_p - curr_p); double cot_beta = cot(curr_p - prev_p, next_p - prev_p); cot_weight = cot_alpha + cot_beta; } cog += cot_weight * mesh.point(*vv_it); valence += cot_weight; } cogs.push_back(cog / valence); } for (v_it = mesh.vertices_begin(), cog_it = cogs.begin(); v_it != v_end; ++v_it, ++cog_it) { if (!mesh.is_boundary(*v_it)) { MyMesh::Point p = mesh.point(*v_it); err = max(err, (p - *cog_it).norm()); mesh.set_point(*v_it, *cog_it); } } return err; }

请注意，代码中使用了 MyMesh 类型，需要先定义和引入该类型，以下是修改后的可运行代码：

#include <OpenMesh/Core/IO/MeshIO.hh>
#include <OpenMesh/Core/Mesh/TriMesh_ArrayKernelT.hh>
#include <vector>

typedef OpenMesh::TriMesh_ArrayKernelT<> MyMesh;

float smoothCot(MyMesh& mesh) {
    float err = -1;
    std::vector<MyMesh::Point> cogs;
    cogs.reserve(mesh.n_vertices());
    MyMesh::VertexIter v_it, v_end;
    MyMesh::VertexVertexIter vv_it;
    MyMesh::Point cog;
    double valence;
    v_end = mesh.vertices_end();
    for (v_it = mesh.vertices_begin(); v_it != v_end; ++v_it) {
        cog[0] = cog[1] = cog[2] = valence = 0.0;
        for (vv_it = mesh.vv_iter(*v_it); vv_it.is_valid(); ++vv_it) {
            double cot_weight = 0.0;
            MyMesh::HalfedgeHandle heh = mesh.find_halfedge(*v_it, *vv_it);
            if (!mesh.is_boundary(heh)) {
                MyMesh::HalfedgeHandle prev_heh = mesh.prev_halfedge_handle(heh);
                MyMesh::HalfedgeHandle next_heh = mesh.next_halfedge_handle(heh);
                MyMesh::VertexHandle prev_vh = mesh.to_vertex_handle(prev_heh);
                MyMesh::VertexHandle next_vh = mesh.to_vertex_handle(next_heh);
                MyMesh::Point prev_p = mesh.point(prev_vh);
                MyMesh::Point curr_p = mesh.point(*v_it);
                MyMesh::Point next_p = mesh.point(next_vh);
                double cot_alpha = cot(prev_p - curr_p, next_p - curr_p);
                double cot_beta = cot(curr_p - prev_p, next_p - prev_p);
                cot_weight = cot_alpha + cot_beta;
            }
            cog += cot_weight * mesh.point(*vv_it);
            valence += cot_weight;
        }
        cogs.push_back(cog / valence);
    }
    std::vector<MyMesh::Point>::iterator cog_it = cogs.begin();
    for (v_it = mesh.vertices_begin(); v_it != v_end; ++v_it, ++cog_it) {
        if (!mesh.is_boundary(*v_it)) {
            MyMesh::Point p = mesh.point(*v_it);
            err = std::max(err, (p - *cog_it).norm());
            mesh.set_point(*v_it, *cog_it);
        }
    }
    return err;
}

int main(int argc, char **argv) {
    MyMesh mesh;
    if (!OpenMesh::IO::read_mesh(mesh, argv[1])) {
        std::cerr << "read error\n";
        return 1;
    }
    std::cout << "smoothCot error: " << smoothCot(mesh) << std::endl;
    if (!OpenMesh::IO::write_mesh(mesh, "output.obj")) {
        std::cerr << "write error\n";
        return 1;
    }
    return 0;
}

其中，cot 函数需要自己实现，如下：

double cot(const MyMesh::Point& v1, const MyMesh::Point& v2) {
    return std::tan(MyMesh::Angle(v1, v2));
}

请注意，以上代码仅供参考，可能存在错误或不足之处，需要结合具体情况进行修改和完善。