gistfile1.cs

        /// <summary>
        /// Gets the position on the current polygon at which the specified edge intersects it.
        /// </summary>
        /// <param name="line"></param>
        /// <returns></returns>
        public Vector3 GetIntersection(Edge3 line)
        {
            // Set up vector variables;
            Vector3 a, b, c, p, q;
            a = this.A.ToVector3();
            b = this.B.ToVector3();
            c = this.C.ToVector3();
            p = line.P.ToVector3();
            q = line.Q.ToVector3();

            // Vector from A to C
            var ex = this.C.X - this.A.X;
            var ey = this.C.Y - this.A.Y;
            var ez = this.C.Z - this.A.Z;

            // Vector from A to B
            var fx = this.B.X - this.A.X;
            var fy = this.B.Y - this.A.Y;
            var fz = this.B.Z - this.A.Z;

            // Cross product of e and f
            var nx = (fy * ez) - (fz * ey);
            var ny = (fz * ex) - (fx * ez);
            var nz = (fx * ey) - (fy * ex);

            // Normalize
            var m = Math.Sqrt((nx * nx) + (ny * ny) + (nz * nz));
            nx /= m;
            ny /= m;
            nz /= m;

            // Ray direction vector
            var dx = line.Q.X - line.P.X;
            var dy = line.Q.Y - line.P.Y;
            var dz = line.Q.Z - line.P.Z;

            m = Math.Sqrt((dx * dx) + (dy * dy) + (dz * dz));
            dx /= m;
            dy /= m;
            dz /= m;

            // Dot product of ray and normal, tells us if ray is pointing towards the triangle.
            m = (dx * nx) + (dy * ny) + (dz * nz);

            // Value of m determines the relationship of the vectors:
            // m < 0: Vectors are opposed
            // m == 0: Vectors are perpendicular
            // m > 0: Vectors point the same way
            if (m < 0)
            {
                var gx = this.A.X - line.P.X;
                var gy = this.A.Y - line.P.Y;
                var gz = this.A.Z - line.P.Z;

                var t = (gx * nx) + (gy * ny) + (gz * nz);

                if (t < 0)
                {
                    var k = t / m;

                    var sx = p.X + (dx * k);
                    var sy = p.Y + (dy * k);
                    var sz = p.Z + (dz * k);

                    return new Vector3(sx, sy, sz);
                }
            }

            throw new NotImplementedException();
            //return null;
        }