Constrained DT, how to keep track of vertex IDs? #7738
Replies: 2 comments 7 replies
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I use these typedef CGAL::Exact_predicates_inexact_constructions_kernel K;
struct FaceInfo2 {
FaceInfo2() {}
int nesting_level;
bool in_domain() { return nesting_level % 2 == 1; }
};
typedef CGAL::Triangulation_vertex_base_with_info_2<int, K> Vbi2;
typedef CGAL::Triangulation_face_base_with_info_2<FaceInfo2, K> Tfbi2;
typedef CGAL::Constrained_triangulation_face_base_2<K, Tfbi2> Ctfb2;
typedef CGAL::Triangulation_data_structure_2<Vbi2, Ctfb2> Tds2;
typedef CGAL::Exact_predicates_tag Itag;
typedef CGAL::Constrained_Delaunay_triangulation_2<K, Tds2, Itag> CDT;This code has not be written with the latest CGAL version, so maybe some things have changed. The type You have to make "marked points", that is to say a pair made of a point and an integer, the id. Something like that: points[i] = std::make_pair(CDT::Point(2, 3), i);Then after inserting the constraints you insert the marked points like this: cdt.insert(points.begin(), points.end());And here is a piece of code showing how to retrieve the ids, they are in for(CDT::Face_handle f : cdt.finite_face_handles()){
if(f->info().in_domain()){
const int id0 = f->vertex(0)->info();
const int id1 = f->vertex(1)->info();
const int id2 = f->vertex(2)->info();
const face_descriptor fd = mesh.add_face(
vertex_descriptor(id0),
vertex_descriptor(id1),
vertex_descriptor(id2)
);
if(fd == Mesh::null_face()) { // that should not happen
exit().......;
}
}
}Sorry for some vagueness. I hope this helps. |
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Getting really close, this almost fully works. Here's my last issue, This code compiles, but once I've added the points here, i don't see how to add the constraints since I'm pretty convinced I need to get the Vertex handles (https://doc.cgal.org/latest/Triangulation_2/classCGAL_1_1Constrained__Delaunay__triangulation__2.html#a4374cf307382b6ceee07db4bdc1e4e61). The And then could reuse the However, this code here doesn't compile: I can also try to insert each polyline individually, using However, I get another one of these quite opaque errors: |
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The constraints must (?) be inserted before the points. At least this is what I do (and it works). Here is the beginning of my code. But I use Rcpp, a C++ library whose purpose is to write C++ code for R. The wording is clear: const int npoints = pts.ncol();
std::vector<std::pair<CDT::Point, int>> points(npoints);
Mesh mesh;
for(int i = 0; i < npoints; ++i) {
const Rcpp::NumericVector pt_i = pts(Rcpp::_, i);
points[i] = std::make_pair(CDT::Point(pt_i(0), pt_i(1)), i);
mesh.add_vertex(Point2(pt_i(0), pt_i(1)));
}
CDT cdt;
{
const size_t nedges = edges.ncol();
for(size_t k = 0; k < nedges; ++k) {
const Rcpp::IntegerVector edge_k = edges(Rcpp::_, k);
cdt.insert_constraint(points[edge_k(0) - 1].first,
points[edge_k(1) - 1].first);
}
}
cdt.insert(points.begin(), points.end());
....... |
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I don't know whether removing the constraints is supposed to perform a regular DT but indeed if this is the case there's something wrong since 40x3=120 and a regular DT does not discard some points. |
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How to retrieve the vertex indices@MartensCedric I am not completely sure, but it seems your code uses the type suggested by @stla, in particular: struct FaceInfo2 {
FaceInfo2() {}
int nesting_level;
bool in_domain() { return nesting_level % 2 == 1; }
};
typedef CGAL::Triangulation_vertex_base_with_info_2<int, K> Vbi2;
typedef CGAL::Triangulation_face_base_with_info_2<FaceInfo2, K> Tfbi2;but your code does not use those extra information correctly. @stla suggested to point all points along with indices, in a container of std::vector<std::pair<Point_CDT_2, size_t>> points;
for(size_t i = 0; i < points.size(); i++)
{
Point_CDT_2 p = uv_segment[i];
points.push_back(std::make_pair(p, i));
}
constrained_dt.insert(points.begin(), points.end());Note that here @stla uses
(Note to @stla: you use Why only 60 faces?Now have a look at the face info used in @stla suggestion: struct FaceInfo2 {
FaceInfo2() {}
int nesting_level;
bool in_domain() { return nesting_level % 2 == 1; }
};If In your loop to display the faces, you have: for(CDT::Face_handle f : constrained_dt.finite_face_handles()) {
if(f->info().in_domain()) {
// [...]
outfile << "f " << id0 << " " << id1 << " " << id2 << std::endl;
}
}the condition |
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Thanks @lrineau @MartensCedric My code was written with an older version of CGAL. The |
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Hey thanks @lrineau and @stla for the help!
I don't fully understand this, looking at @stla 's code: The part related to the insertion can be simplified to: ...
std::vector<std::pair<CDT::Point, int>> points(npoints);
...
cdt.insert(points.begin(), points.end());And comparing it to mine std::vector<std::pair<Point_CDT_2, size_t>> all_points_info(segment_points.begin(), segment_points.end());
for(int i = 0; i < uv_sphere_info.size(); i++)
{
all_points_info.push_back(uv_sphere_info[i]);
}
constrained_dt.insert(all_points_info.begin(), all_points_info.end());As, far as I can tell, we're using the same overload. So I'm not sure what you mean by |
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You are right. You have used the right code to insert the points with the indices. I do not know why I thought otherwise. Just forget that part of my message, and focus only on the section "Why only 60 faces?". Sorry for that. |
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One issue I'm getting over and over with CGAL is I'm always having difficulties keeping track of vertex ids. This is a major pain point in my workflow, for example I have a CDT where I want to keep track of the vertex IDs:
I get this error, I'm not sure what I'm missing and I'm struggling to find examples
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