Object retrieval apparatus and object retrieval method

An object retrieval method executed by a computer, comprising:

• dividing a sight range into a plurality of pieces according to distance from a sight point in a three dimensional space:
• assigning a different one of the first to N-th space index information to each divided range such that a smaller index number of space index information of the first to N-th space index information is assigned to the divided range closer to the sight point wherein the first to N-th space index information include information relating to X1 objects to XN (where N is an integer of 2 or greater) objects each set of which are selected in a descending order of an object size from among a plurality of objects disposed in three dimensional space, and in which a value of XT (where T is a value from 1 to N) decreases as a value of T increases;
• and
• specifying an object having a size visible from the sight point among objects existing in each divided range by retrieving the space index information assigned to each divided range.