Some range queries supported by R* tree could be
translated into general range queries with some post processing.
For example, to find out some restaurants around some
coordinates of with a distance less than 1 kilometer,
the range query should select the restaurants in a circle with a
diameter of 1 kilometer which could be answered by a R* tree
index. However, we can build a query condition that is a
superset of the original query condition. The query condition
takes the form of x1