Abstract: A solid modelling system for generating a spatial representation of an object defined by a structure having a plurality of linked nodes representing the object in terms of solid geometric primitives combined by a logical expression, which is adapted to recognize redundant primitives automatically. Bitmap generation logic (BGL) is provided for traversing at least certain of the nodes in the structure for generating a bitmap representing the part of the logical expression defined in the traversed nodes and redundant primitive logic (RPL) is provided for testing the bitmap for logical redundancies indicative of redundant geometric primitives. Each bit in the bitmap is representative of a respective one of the constituents of the primitives, a constituent being the volume formed by the intersection of primitives or their complements, and, in order to test for the redundancy of a primitive u, the RPL tests for equivalence of the corresponding utrue and ufalse constituents in the bitmap.