Why doesn't this implementation of Jarvis' March (“Gift wrapping algorithm”) work?

Question

I\'m trying to implement Jarvis\' algorithm for finding the convex hull of a set of points, but for some reason it doesn\'t work. This is my implementation:

proc         


        

Answer 1

The loop adds using this line of code:

aHull.Add(vPointOnHull);

vPointOnHull is only assigned in these lines:

vPointOnHull := Self.LeftMostPoint;
vPointOnHull := vEndpoint;

You already explained that LeftMostPoint is added correctly, so the repeat must come from vEndPoint, which is assigned in these lines:

vEndpoint := Self.Point[0];
vEndpoint := Self.Point[I];

So I guess the last assignment (which is in the below if statement), is never reached.

  if Orientation(vPointOnHull,vEndpoint,Self.Point[I]) = LeftHandSide then
    vEndpoint := Self.Point[I];

--jeroen