Delaunay triangulation in C++ from lua

Question

I'm trying to implement a simple Delaunay Triangulation, from the lua file in the zip archive to C++.

#include "delaunay.h"

#include <cmath>
#include <algorithm>  
#include <assert.h>

std::vector<Triangle> Delaunay::triangulate(std::vector<Vector2<float>> points)
{
    std::size_t npoints = points.size();
    int trmax = npoints * 4;

    float minX = points[0].getX();
    float minY = points[0].getY();
    float maxX = minX;
    float maxY = minY;

    for(std::size_t i = 0; i < points.size(); ++i) {
        points[i].id = i;
        if (points[i].getX() < minX) 
            minX = points[i].getX();
        if (points[i].getY() < minY)
            minY = points[i].getY();
        if (points[i].getX() > maxX)
            maxX = points[i].getX();
        if (points[i].getY() > maxY)
            maxY = points[i].getY();
    }

    float dx = maxX - minX;
    float dy = maxY - minY;
    float deltaMax = std::max(dx, dy);
    float midx = (minX + maxX) * 0.5;
    float midy = (minY + maxY) * 0.5;


    Vector2<float> p1(midx - 2 * deltaMax, midy - deltaMax);
    Vector2<float> p2(midx, midy + 2 * deltaMax);
    Vector2<float> p3(midx + 2 * deltaMax, midy - deltaMax);

    p1.id = npoints + 1;
    p2.id = npoints + 2;
    p3.id = npoints + 3;

    points.push_back(p1);
    points.push_back(p2);
    points.push_back(p3);

    std::vector<Triangle> triangles;
    triangles.push_back(Triangle(points[points.size() - 1], points[points.size() - 2], points[points.size() - 3]));

    for(std::size_t i = 0; i < npoints; ++i) {
        std::vector<Edge> edges;

        for(std::size_t j = triangles.size(); j-- > 0; ) {
            Triangle curTriangle = triangles[j];

            if(curTriangle.inCircumCircle(points[i])) {
                edges.push_back(curTriangle.getE1());
                edges.push_back(curTriangle.getE2());
                edges.push_back(curTriangle.getE3());
                triangles.erase(triangles.begin() + j);
            }
        }

        for(std::size_t j = edges.size() - 1; --j > 0; ) {
            for(std::size_t k = edges.size(); --k > j + 1; ) {
                if(edges[j].equals(edges[k])) {
                    edges.erase(edges.begin() + j); 
                    edges.erase(edges.begin() + k - 1);
                }
            }   
        }

        for(std::size_t j = 0; j < edges.size(); ++j) {
            int n = triangles.size();
            std::cout << n << " " << trmax << std::endl;
            assert(n <= trmax && "Generated more than needed triangles");   
            triangles.push_back(Triangle(edges[j].getP1(), edges[j].getP2(), points[i]));
        }
    }

    for(std::size_t i = triangles.size(); --i > 0; ) {
        Triangle triangle = triangles[i];
        if(triangle.getP1().id > static_cast<int>(npoints) ||
            triangle.getP2().id > static_cast<int>(npoints) ||
            triangle.getP3().id > static_cast<int>(npoints)) {
            triangles.erase(triangles.begin() + i);
        }
    }

    return triangles;
}

And here's what I got

/usr/bin/../lib64/gcc/x86_64-unknown-linux-gnu/5.2.0/../../../../include/c++/5.2.0/debug/vector:406:
error: attempt to subscript container with out-of-bounds index 29, but 
container only holds 29 elements.

Objects involved in the operation:
    sequence "this" @ 0x0x7ffd71c01260 {
}
[1]    31657 abort (core dumped)  ./pudding

The problem is that I keep getting a load of out of bound indices, and when it works, the assert at the line 77 in the hastebin makes it crash.

This line is making it crash

if(edges[j].equals(edges[k]))

Does anyone have an idea why is it not working? All the files are here if you want to take a look.

Thanks a lot.

Please include the code inside of the question itself, not as an external link. Please also provide sample input, and the exact error messages that you get. — Colonel Thirty Two, Oct 05 '15 at 21:31
I tried, but the indentation was way worst, so it's better with a hastebin, plus there's a syntax highlight — bl4ckb0ne, Oct 05 '15 at 21:35

Micromega · Answer 1 · 2015-10-06T07:19:39.180

0

When you generate new triangles you seem to include edges with the current point. This give the error. Make the new triangles vertices not all the current point.

edited Oct 06 '15 at 07:19

answered Oct 06 '15 at 07:01

Micromega

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I don't understand what you're saying. Which points shoud I give to the constructor? – bl4ckb0ne Oct 06 '15 at 17:35
It's a rare condition but when you form new triangles with the new point it can happen the next point is in the circumcenter of 1 to many triangles. It is not easy computation. It can take long time. – Micromega Oct 06 '15 at 18:50

Delaunay triangulation in C++ from lua

1 Answers1