Accelerating the evaluation of volumetric modelers by manipulating CSG trees and DAGs

doi:10.1016/0010-4485(91)90010-T

Computer-Aided Design

Volume 23, Issue 6, July–August 1991, Pages 420-434

https://doi.org/10.1016/0010-4485(91)90010-T Get rights and content

Abstract

A CSG-based interface is commonly used in CAD systems as the main technique for defining objects. The CSG definition (trees or dags) is used regardless of the internal representation scheme, and it is particularly popular with volumetric geometric modelers (e.g. octree-encoding and switching-function based representation). The resources required to generate the volumetric code depend on the specific CSG definition, which may contain operations that are expensive to perform with the volumetric representation. As the CSG definition is not unique, it can be manipulated to obtain an equivalent CSG definition that is more suitable for generating the volumetric code.

The paper presents methods that eliminate costly operations from the internal nodes of a CSG definition, and transfer them to the level of the leaves (where they are not expensive to perform), before the volumetric code is generated. A consequent reduction is achieved in the resources required to generate the volumetric code.

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There are more references available in the full text version of this article.

Cited by (1)

Separation of disconnected machining regions on the basis of a CSG model
1994, Computer-Aided Design
The process of converting a given design into the form of a rawstock minus a series of machining features is known as machining-features extraction. One step towards automatic machining-features extraction is the extraction of machining regions. The paper is concerned with the extraction of machining regions from the constructive-solid-geometry representation of a given object.
The proposed method for the extraction of machining regions is based on manipulating the original CSG tree, representing the object, evaluating the various machining regions by using octrees, and pruning the CSG tree accordingly. If necessary, an additional stage of compacting follows. As a result, each machining region is represented by a compact CSG tree offering the following advantages. The CSG tree to be analysed is reduced in size, and thus the problem of machining-features extraction is simplified. The information is compact and concise. Moreover, no information is lost (CSG representation is kept rather than boundary representation), and the designer's intensions are conveyed to the process planner more clearly.
In the special case in which the machining regions are identical to machining features, the method does offer the automatic extraction of machining features. In addition, the nesting level of the various machining regions is determined when needed.

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Accelerating the evaluation of volumetric modelers by manipulating CSG trees and DAGs

Abstract

Comput. Graph. & Image Proc.

Annals CIRP

The PADL-1.0/2 system for defining and displaying solid objects

Comput. Graph.

Representations for rigid solids: theory, methods and systems

ACM Comput. Surveys

Solid modelling: a historical summary and contemporary assessment

IEEE Comput. Graph. & Applic.

An Introduction to Solid Modeling

Geometric Modeling