Eureka! exstatica! There is a better way, The ellipse has 2 focal points F1 and F2 and a "length", where the pencil is, when drawing ellipses the classical way. If the point you are checking is further away from that length, then it is outside the ellipse. So: segment length from (x,y) to F1(x,y) PLUS segment length from (x,y) to F2(x,y) must not exceed "length", if it does, it is outside. Thus, the length is 4 sums and an abs, much much faster than polygons... will elaborate later (at work right now)