def h(self, child_node: Node):
"""
Estimate the cost of the cheapest path from the next node to the destination node.
Calculate the heuristic.
:param child_node: Child node from where the heuristic should be calculated.
"""
(x1, y1, z1) = child_node.position
(x2, y2, z2) = self.dest_node.position
child_node.h = abs(x1 - x2) + abs(y1 - y2) + abs(z1 - z2)
