CellBase needs the following member functions:
- Rcoord_t get_pixel_coordinate(const Ccoord & pixel) const returning the real space coordinates of the center of pixel pixel
- Rcoord_t get_pixel_lengths() const returning the physical dimension of a pixel
- bool is_inside(Rcoord_t point) as well as bool is_inside(Ccoord_t pixel) that check whether a pixel or point lie within the cell or not.