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.
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. 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.