Solid modelling system with logic to discard redundant primitives

• US 5,086,495 A
• Filed: 12/16/1988
• Issued: 02/04/1992
• Est. Priority Date: 12/18/1987
• Status: Expired due to Fees

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Gray, Michael A., Halbert, Alan R., Todd, Stephen J.
• Primary Examiner(s): Harkcom, Gary V.
• Assistant Examiner(s): Bayer, Raymond J.
• Application Number:
  US07/285,850
• Time in Patent Office: 1,145 Days
• Field of Search: 364/522, 364/518, 364/521, 364/488, 364/512, 364/578, 340/729, 340/747
• US Class Current: 345/420
• CPC Class Codes: G06T 17/20 Finite element generation, e.g. wire-frame surface description, tesselation

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. The BGL additinally generates a table of pointers to the primitives encountered during the traversal and the RPL deletes from the table a pointer to a primitive which is found to be redundant. Node generation logic (NGL) is provided for replacing the nodes traversed by the first logic by a single truth table node which comprises the modified bitmap produced by the RPL and pointers to nodes defining the remaining primitives. Logic may also be provided for processing a relevance map indicative of geometric information in combination with the bitmap.

Claims

1. A solid modelling system for generating a spatial representation of an object defined in terms of solid geometric primitives combined by a logical expression including one or more combinatorial logical operators, comprising:

object definition means including a structure comprising a plurality of linked nodes for said primitives and for said operators;

first logic means for traversing at least certain of the nodes generating a table comprising a bitmap representing the logical expression or the part thereof defined at the operator nodes encountered during the traversal; and

second logic means for testing the bitmap for logical redundancies indicative of redundant geometric primitives.

2. A solid modelling system as claimed in claim 1 wherein each bit in the bitmap is representative of a respective one of the constituents of said primitives and wherein said second logic means, in order to test for the redundancy of a primitive u, tests for the equivalence of corresponding utrue and ufalse constituent in the bitmap.

3. A solid modelling system as claimed in claim 1 wherein said first logic means additionally generates a set of pointers to the primitives encountered during the traversal and wherein the second logic deletes from the set a pointer to a primitive which is found to be redundant.

4. A solid modelling system as claimed in claim 3 additionally comprising third logic means for replacing the nodes traversed by said first logic means by a single truth table node which comprises the bitmap produced by said first logic means and the set of pointers to nodes defining the remaining primitives.

5. A solid modelling system as claimed in claim 4 which additionally comprises:

world space definition means for defining a voxel in which the object exists;

spatial subdivision logic means for subdividing world space into progressively smaller voxels until voxels are created for which the spatial representation can be rendered;

object simplification logic means for simplifying the structure defining the object within a voxel generated by the spatial subdivision means by combining or eliminating primitives entirely inside or outside said voxel;

counting logic means for counting the number of primitives remaining in the, or a part of a simplified structure as generated by the object simplification means and, if there are less than a predetermined number of primitives, to cause the first and second logic means to process said simplified structure.

6. A solid modelling system as claimed in claim 5 in which the object simplification logic means comprises:

logic which, within a voxel generated by said spatial subdivision logic means simplifies the truth table node previously inserted in the structure by the third logic means.

7. A solid modelling system as claimed in claim 5, additionally comprising logic for processing a relevance map representative of geometric information for indicating when bits of the bitmap are determined to be irrelevant to the definition of the object within that voxel.

8. A solid modelling system as claimed in claim 7, wherein said second logic means deletes from the set of pointers a pointer to a primitive by modifying the relevance map.

9. A solid modelling system as claimed in claim 1 which additionally comprises:

world space definition means for defining a voxel in which the object exists;

spatial subdivision logic means for subdividing world space into progressively smaller voxels until voxels are created for which the spatial representation can be rendered;

object simplification logic means for simplifying the structure defining the object within a voxel generated by the spatial subdivision means by combining or eliminating primitives entirely inside or outside said voxel;

counting logic means for counting the number of primitives remaining in the, or a part of a simplified structure as generated by the object simplification means and, if there are less than a predetermined number of primitives, to cause the first and second logic means to process said simplified structure.

10. A solid modelling system as claimed in claim 9 additionally comprising logic for processing a relevance map representative of geometric information for indicating when bits of the bitmap are determined to be irrelevant to the definition of the object within that voxel.