Hi

I have a line segment intersection method which i translated from JavaScript to C#. But it seems to be hit or miss on success rate on whether it detects an intersection of two lines. I don't know why this is.

This is my method:

        public static bool LineSegementsIntersect(Vector3 p0, Vector3 p1, Vector3 p2, Vector3 p3, out Vector3 intersection)
        {
            intersection = Vector3.zero;

            float A1 = p1.z - p0.z;
            float B1 = p0.x - p1.x;
            float C1 = A1 * p0.x + B1 * p0.z;
            float A2 = p3.z - p2.z;
            float B2 = p2.x - p3.x;
            float C2 = A2 * p2.x + B2 * p2.z;
            float denominator = A1 * B2 - A2 * B1;
            if (Mathf.Approximately(denominator, 0))
            {
                return false;
            }

            intersection = new Vector3((B2 * C1 - B1 * C2)/denominator,0f,(A1*C2 - A2*C1)/denominator);
            return true;
        }

And my test data has:

    if (Maths.LineSegementsIntersect(start,end, A.Position, B.Position, out intersectingPoint))
    {
        Debug.Log(start+":"+end+" intersects "+A.Position+":"+B.Position+ " at: "+intersectingPoint);
        return true;
    }

And my console gives me true for:

(0.0, 0.0, 0.0):(0.0, 0.0, 1.0) intersects (13.0, 0.0, 9.0):(22.0, 0.0, 9.0) at (0.0, 0.0, 9.0)

This is clearly incorrect. Yet i get true and i have no idea why that is.

It looks like your segment intersection test is actually an infinite line test. It will only return false if they are parallel or coincident...

It looks like your segment intersection test is actually an infinite line test. It will only return false if they are parallel or coincident...

You're right i am an idiot! I have solved it now i realised that mistake ! oops :P