Reducing index size for multi-level grid indexes

1. A computer-implemented method of querying an index of first objects comprised of a plurality of cells index entries and a pool of second objects, the method comprising:

evaluating the index of the first objects to produce a group of one or more candidates based on whether one or more index entries of the first objects satisfy cells designated in a query that respective first objects in the index overlap;

adding second objects from the pool to said group of candidates to produce an interim group of candidates;

filtering the interim group of candidates by comparing the query with approximations of the candidates of the interim group with the query to produce filtered candidate objects;

determining if the filtered candidate objects satisfy the query by comparing the first and second objects corresponding to the filtered candidate objects with the query; and

in response to determining that the filtered candidate objects satisfy the query, returning a result.

2. The computer-implemented method of claim 1 , wherein the index is a grid index comprised of a plurality of grid cells, the first and second objects are geometric shapes, and the second objects are larger than the first objects.

3. The computer-implemented method of claim 2 , wherein all geometric shapes from the pool are added to said group of candidates to produce the interim group of candidates.

4. The computer-implemented method of claim 2 , wherein the approximations of the candidate objects are minimum bounding rectangles of the geometric shapes corresponding to the candidate objects.

5. The computer-implemented method of claim 4 , wherein said determining if the filtered candidate objects satisfy the query includes comparing the geometric shapes corresponding to the filtered candidate objects with a query area specified in the query.

6. A computer-readable storage medium storing a computer program for querying an index of first objects comprised of a plurality of cells and a pool of second objects, the computer program having program instructions, that, when executed by a processor of a computer perform:

evaluating the index of the first objects to produce a group of one or more candidates based on whether one or more index entries of the first objects satisfy cells designated in a query that respective first objects in the index overlap;

adding second objects from the pool to said group of candidates to produce an interim group of candidates;

filtering the interim group of candidates by comparing the query with approximations of the candidates of the interim group with the query to produce filtered candidate objects;

determining if the filtered candidate objects satisfy the query by comparing the first and second objects corresponding to the filtered candidate objects with the query; and

in response to determining that the filtered candidate objects satisfy the query, returning a result.

7. The computer-readable storage medium of claim 6 , wherein the index is a grid index comprised of a plurality of grid cells, the first and second objects are geometric shapes, and the second objects are larger than the first objects.

8. The computer-readable storage medium of claim 7 , wherein all geometric shapes from the pool are added to said group of candidates to produce the interim group of candidates.

9. The computer-readable storage medium of claim 7 , wherein the approximations of the candidate objects are minimum bounding rectangles of the geometric shapes corresponding to the candidate objects.

10. The computer-readable storage medium of claim 9 , wherein said determining if the filtered candidate objects satisfy the query includes comparing the geometric shapes corresponding to the filtered candidate objects with a query area specified in the query.

11. A computer system for querying an index of first objects comprised of a plurality of cells index entries and a pool of second objects, comprising:

a processor;

a storage medium;

means for evaluating the index of the first objects to produce a group of one or more candidates based on whether one or more index entries of the first objects satisfy cells designated in a query that respective first objects in the index overlap;

means for adding second objects from the pool to said group of candidates to produce an interim group of candidates;

means for filtering the interim group of candidates by comparing the query with approximations of the candidates of the interim group with the query to produce filtered candidate objects;

means for determining if the filtered candidate objects satisfy the query by comparing the first and second objects corresponding to the filtered candidate objects with the query; and in response to determining that the filtered candidate objects satisfy the query, returning a result.

12. The computer system of claim 11 , wherein the index is a grid index comprised of a plurality of grid cells, the first and second objects are geometric shapes, and the second objects are larger than the first objects.

13. The computer system of claim 12 , wherein all geometric shapes from the pool are added to said group of candidates to produce the interim group of candidates.

14. The computer system of claim 12 , wherein the approximations of the candidate objects are minimum bounding rectangles of the geometric shapes corresponding to the candidate objects.

15. The computer system method of claim 14 , wherein said determining if the filtered candidate objects satisfy the query includes comparing the geometric shapes corresponding to the filtered candidate objects with a query area specified in the query.