Method for immediate boolean operations using geometric facets
CAFCFirst Claim
1. A method that performs immediate Boolean operations using geometric facets of geometric objects implemented in a computer system and operating with a computer, the method comprising:
 mapping rendering facets to extended triangles that contain neighbors;
building intersection lines starting with and ending with searching for the first pair of triangles that hold a start point of an intersection line by detecting whether two minimum bounding boxes overlap and performing edgetriangle intersection calculations for locating an intersection point, then searching neighboring triangles of the last triangle pair that holds the last intersection point to extend the intersection line until the first intersection point is identical to the last intersection point of the intersection line ensuring that the intersection line gets closed or until all triangles are traversed;
splitting each triangle through which an intersection line passes using modified Watson method, wherein the modified Watson method includes removing duplicate intersection points, identifying positions of end intersection points, and splitting portion of each triangle including an upper portion, a lower portion, and a middle portion;
checking each triangle whether it is obscure or visible for Boolean operations or for surface trimming;
regrouping facets in separate steps that includes copying triangles, deleting triangles, reversing the normal of each triangle of a geometric object, and merging reserved triangles to form one or more new extended triangle sets; and
mapping extended triangles to rendering facets.
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Abstract
A method for performing Boolean operations using a computer to create geometric models from primary geometric objects and their facets, comprises mapping rendering facets to extended triangles that contain neighbors; building intersection lines, splitting each triangle through which an intersection line passes, determining each facet is visible or obscure, and regrouping the facets to form one or more geometric objects. This method does not utilize the most popular data structures CSG and BREP in CAD/CG/Solid Modeling systems, but has the advantages of both CSG and BREP: easy to implement and flexible. Additionally it is a united method for solid modeling and surface modeling systems, and it is able to generate variant and editable models.
27 Citations
20 Claims

1. A method that performs immediate Boolean operations using geometric facets of geometric objects implemented in a computer system and operating with a computer, the method comprising:

mapping rendering facets to extended triangles that contain neighbors; building intersection lines starting with and ending with searching for the first pair of triangles that hold a start point of an intersection line by detecting whether two minimum bounding boxes overlap and performing edgetriangle intersection calculations for locating an intersection point, then searching neighboring triangles of the last triangle pair that holds the last intersection point to extend the intersection line until the first intersection point is identical to the last intersection point of the intersection line ensuring that the intersection line gets closed or until all triangles are traversed; splitting each triangle through which an intersection line passes using modified Watson method, wherein the modified Watson method includes removing duplicate intersection points, identifying positions of end intersection points, and splitting portion of each triangle including an upper portion, a lower portion, and a middle portion; checking each triangle whether it is obscure or visible for Boolean operations or for surface trimming; regrouping facets in separate steps that includes copying triangles, deleting triangles, reversing the normal of each triangle of a geometric object, and merging reserved triangles to form one or more new extended triangle sets; and mapping extended triangles to rendering facets.  View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)


11. A computer system consisting of hardware and software that performs immediate Boolean operations using rendering facets of geometric objects, the system comprising:

a computer with input devices for entering data and commands, and a display device showing user interface, geometric objects, and additional data, having a medium storing geometric data and instructions that make up of a software system, or having a microchip or integrated circuit embedding partially or totally the instructions, and a processor that executes the steps of; creating, modifying or loading primary geometric objects including swept and extruded ones and relocating them at different positions or orientations with input devices of the computer; selecting two of the geometric objects; mapping rendering facets to extended triangles that contain neighbors; building intersection lines starting with and ending with searching for the first pair of triangles that hold a start point of an intersection line by detecting whether two minimum bounding boxes overlap and by performing edgetriangle intersection calculations for locating an intersection point, then searching neighboring triangles of the last triangle pair that holds the last intersection point to extend the intersection line until the first intersection point is identical to the last intersection point of the intersection line ensuring that the intersection line gets closed or until all triangles are traversed; splitting each triangle through which an intersection line passes using modified Watson method, wherein the modified Watson method includes removing duplicate intersection points, identifying positions of end intersection points, and splitting portion of each triangle including an upper portion, a lower portion, and a middle portion; checking each triangle whether it is obscure or visible for Boolean operations or for surface trimming; regrouping facets in separate steps that includes copying triangles, deleting triangles, reversing the normal of each triangle of a geometric object, and merging reserved triangles to form one or more new extended triangle sets; and mapping extended triangles to rendering facets.  View Dependent Claims (12, 13, 14, 15, 16, 17, 18, 19, 20)

1 Specification