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Browse Prior Art Database

Collection of Edges Into Polygons in Fast Drawing System

IP.com Disclosure Number: IPCOM000120660D
Original Publication Date: 1991-May-01
Included in the Prior Art Database: 2005-Apr-02
Document File: 2 page(s) / 95K

Publishing Venue

IBM

Related People

Halbert, A: AUTHOR [+2]

Abstract

The construction of a faceted polygon representation of a solid model by collecting edges generated on the surface of the model. Constructive Solid Geometry (CSG) Models are converted into Boundary Representation (BREP) Models of three-dimensional (3D) objects.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Collection of Edges Into Polygons in Fast Drawing System

      The construction of a faceted polygon representation of a
solid model by collecting edges generated on the surface of the
model.  Constructive Solid Geometry (CSG) Models are converted into
Boundary Representation (BREP) Models of three-dimensional (3D)
objects.

      Systems that convert constructive solid geometry models to an
approximate graphics representation may generate a set of
intersection edges.  Disclosed is how these intersection edges may be
collected into a set of polygons to permit surface rendering of a
model by appropriate hardware.  The description is in terms of
FASTDRAW, a derivative of WINSOM (Winchester Solid Modeller)
rendering prototype, and to Winsom90.  It could also apply to similar
systems such as CATIA.

      FASTDRAW consists of two major layers of processing. The higher
level breaks down a complete model valid in all space to a set of
simple models, each valid in a particular voxel.  This level operates
by recursive subdivision and is mostly common code to WINSOM.  The
lower level looks at the simplified models in each voxel and
generates edges on the model, as described in [*].  Edge generation
is implemented in DOTLINE.  These edges may be drawn directly, as by
the original FASTDRAW, or the picture may be improved where
appropriate hardware is available by collecting these edges into
polygons that lie on the surface of the object.

      Edges are collected into polygons on a per voxel basis. At the
start of each voxel, collection is initialized by VOXBEGIN, in
DOTPOLY.  All edges for the voxel are then generated as described in
-*-.  Each edge is a segment of the intersection of two planes.  Each
plane is either a planar approximation to a primitive or a voxel
face.  Each edge segment lies on one of the intersection of two
primitive approximations, called type 1 edge segment, or the
intersection of a primitive approximation with a voxel face, called
type 2 edge segment.  We associate with each edge segment four
planes:  one intersection plane, prim_orig; the other intersection
plane, other_prim;  the plane that defines one end of the edge
segment, from_prim;  and the plane that defines the other end of the
edge segment,...