Cartesian coordinates

If the two objects have Cartesian coordinates $x_{1},y_{1}$ and $x_{2},y_{2}$ then the criterion is simply that $D$ should be less than or equal to the Pythagorean distance between the two points:

$$D \leq \sqrt{ (x_{1} - x_{2})^{2} + (y_{1} - y_{2})^{2} }$$ (7)