This distance can be seen as the approximation of the distance from a point in the 2D space to a
normalized ellipse (normalized means centered in origin and not rotated). From the distance definition of (5)
it turns out that its value is equal or less than 0 if x
r
is inside the hypothesis h , and greater than 0 if it is
outside. Therefore, considering the hand hypothesis h and a point x
r
belonging to a blob b , if the distance
is equal or less than 0, we conclude that the blob b supports the existence of the hypothesis h and it is
selected to represent the new hand state. This tracking process could also detect the presence or the absence
of the hand in the image