TimeCostPedestrianDensityIteration return cost for the pedestrian density by
using the gaussian formula from Seitz paper. We currently use the
getSpatialMapPeds for getting the neighbours (3 * size x size * 3), with size
= 3. The function is for the purpose of navigation around groups.
This implementation is not efficient, but was used to compare the values and
the performance of the different implementations. Use the
TimeCostPedestrianDensity instead.