insert method
Adds an item to the index which is associated with the given interval
@param min the lower bound of the item interval @param max the upper bound of the item interval @param item the item to insert
@throws IllegalStateException if the index has already been queried
Implementation
void insert(double min, double max, Object item) {
if (root != null)
throw new StateError("Index cannot be added to once it has been queried");
leaves.add(new IntervalRTreeLeafNode(min, max, item));
}