How to determine if a point is within a quadrilateral?

Question

**Goal** I want to determine if a test point is within a defined quadrilateral. I'm probably going to implement the solution in Matlab so I only need pseudo-code. **Inputs** Corners of quadrilateral : (x1,y1) (x2,y2) (x3,y3) (x4,y4) Test point : (xt, yt) **Output** 1 - If within quadrilateral 0 - Otherwise **Update** It was pointed out that identifying the vertices of the quadrilateral is not enough to uniquely identify it. You can assume that the order of the points determines the sides of the quadrilateral (point 1 connects 2, 2 connects to 3, 3 connects to 4, 4 connects to 1)

Answer 1

draw a horizontal line from the point to infinity so as to guarantee that it clears the polygon.

If the horizontal line intersects the polygon in an odd number of points, then it is inside.