Is a point inside a 4 point polygon?

Given two point I am drawing some kind of rectangle(It should be a rectangle but there is a slight error).
As my somehow rectangle is not a real rectangle - Creating a rectangle out of this point and using rectangle.contains has some errors and what you see isn't what you get(you see a point in the rectangle but actually it isn't).

Any idea for a solution?


Can you please describe a little more about what you are trying to do, or can you provide a code example? I don’t quite understand.