Hi all!

I have found Andrew's monotone convex hull algorithm implemented on the net:

Algorithm Implementation/Geometry/Convex hull/Monotone chain - Wikibooks, open books for an open world

This is perfect for me, but I have an irritating problem... I just can't figure out how to use the stuct Point. Here's the implementation:

If i for example want to use the method cross(), then what do I write? This seems the most logical: cross(1.1, 3.9, 11.0), but this is read as doubles.Code:// Implementation of Andrew's monotone chain 2D convex hull algorithm. // Asymptotic complexity: O(n log n). // Practical performance: 0.5-1.0 seconds for n=1000000 on a 1GHz machine. #include <algorithm> #include <vector> using namespace std; typedef int coord_t; // coordinate type typedef long long coord2_t; // must be big enough to hold 2*max(|coordinate|)^2 struct Point { coord_t x, y; bool operator <(const Point &p) const { return x < p.x || (x == p.x && y < p.y); } }; // 2D cross product of OA and OB vectors, i.e. z-component of their 3D cross product. // Returns a positive value, if OAB makes a counter-clockwise turn, // negative for clockwise turn, and zero if the points are collinear. coord2_t cross(const Point &O, const Point &A, const Point &B) { return (A.x - O.x) * (B.y - O.y) - (A.y - O.y) * (B.x - O.x); } // Returns a list of points on the convex hull in counter-clockwise order. // Note: the last point in the returned list is the same as the first one. vector<Point> convex_hull(vector<Point> P) { int n = P.size(), k = 0; vector<Point> H(2*n); // Sort points lexicographically sort(P.begin(), P.end()); // Build lower hull for (int i = 0; i < n; i++) { while (k >= 2 && cross(H[k-2], H[k-1], P[i]) <= 0) k--; H[k++] = P[i]; } // Build upper hull for (int i = n-2, t = k+1; i >= 0; i--) { while (k >= t && cross(H[k-2], H[k-1], P[i]) <= 0) k--; H[k++] = P[i]; } H.resize(k); return H; }

I don't want to use the cross method of cause, just to understand how Points are written, so I can supply the convex_hull method with a vector containing these Points.

Best regards

Jannick