Get the zone that encompasses the point v. The optional value start can be given to seed the search with the last zone found at that point. This zone is checked first and will be the only zone checked if valid, speeding up the check.
- Returns:
z - the pointer to the zone containing the point being checked, or null if no zone is found
- Arguments:
v - the point in space being checked
start - optional starting zone to check first
9.1.13