convex-hull

Given a set of points S (x, y, z) . How to find the convex hull of those points ? I tried understanding the algorithm from here , but could not get much. It says: First project all of the points onto the xy-plane, and find an edge that is definitely on the hull by selecting the point with highest y-coordinate and then doing one iteration of gift wrapping to determine the other endpoint of the edge. This is the first part of the incomplete hull. We then build the hull iteratively. Consider this first edge; now find another point in order to form the first triangular face of the hull. We do this

I would be grateful to you if you could help me with this issue :) Relating to this question cvConvexityDefects in OpenCV 2.X / C++? , I have the same problem. The OpenCV C++ wrapper has not the function cvConvexityDefects that appears in the C version, so I tried to write my own version. Part of the code is (please note that both countour and hull are vector< Point >, calculated separately : CvSeq* contourPoints; CvSeq* hullPoints; CvSeq* defects; CvMemStorage* storage; CvMemStorage* strDefects; CvMemStorage* contourStr; CvMemStorage* hullStr; CvConvexityDefect *defectArray = 0; strDefects =

Suppose I have an array of points in random order, and I need to find a polygon (by sorting them, such that every adjacent pair represents a side) which passes through all of the points, and its sides are non-intersecting of course. I tried to do it by selecting a point, and adding all points to the final array which are below it, sorted left to right. Then, adding all points which are above it, sorted right to left. I've been told that I can add an additional point and sort naturally to avoid self-intersections.. I am unable to figure out that though. What's a simple way to do this? As

I have a set of points. I want to separate them into 2 distinct sets. To do this, I choose two points ( a and b ) and draw an imaginary line between them. Now I want to have all points that are left from this line in one set and those that are right from this line in the other set. How can I tell for any given point z whether it is in the left or in the right set? I tried to calculate the angle between a-z-b – angles smaller than 180 are on the right hand side, greater than 180 on the left hand side – but because of the definition of ArcCos, the calculated angles are always smaller than 180°.

I have a point cloud of coordinates in numpy. For a high number of points, I want to find out if the points lie in the convex hull of the point cloud. I tried pyhull but I cant figure out how to check if a point is in the ConvexHull : hull = ConvexHull(np.array([(1, 2), (3, 4), (3, 6)])) for s in hull.simplices: s.in_simplex(np.array([2, 3])) raises LinAlgError: Array must be square. Juh_ Here is an easy solution that requires only scipy: def in_hull(p, hull): """ Test if points in `p` are in `hull` `p` should be a `NxK` coordinates of `N` points in `K` dimensions `hull` is either a scipy