Push-pull direct modeling of solid CAD models

Abstract

Direct modeling is a very recent CAD modeling paradigm featuring direct, intuitive push-pull interactions with the geometry of the model to much increase model editing flexibility. The major issue for push-pull direct modeling is the possible inconsistency between the altered geometry of the model and its unchanged topology. The challenge of resolving the geometry-topology inconsistency lies in ensuring that the resulting model remains as a valid solid model and that the model shape follows a continuous change pattern. Although push-pull direct modeling has been implemented in several CAD software packages, robustness towards generating valid modeling results and continuous shape changes still remains an open issue. This paper proposes a systematic method to handle the resolution of any possible inconsistent situation. The method formulates the continuous shape change requirement as successive Boolean operations on the model volume, thereby guaranteeing valid solid models and continuous shape changes. Further, this formulation allows an easy implementation of push-pull direct modeling using existing CAD research and engineering results. In order to show the effectiveness of the proposed method, a software prototype is developed and the modeling results are compared with those of five leading CAD software packages.

Parametric/direct CAD integration

“…The essential advance made is: tweaking does not allow any violations to the pre-edit model topology, while push-pulling allows such violations. With this relaxation, direct modeling achieves much improved modeling flexibility, refer to [21,22] for examples. The early version of direct modeling consisted primarily of push-pull operations.…”

“…This is essentially achieved by discarding the use of associativity and making all geometric entities in a solid model free to change. Typically, users just need to grab, push, and pull the geometric entities of interest so as to make desired changes [21,22]. With this geometry-oriented strategy, users can directly edit the model as they see fit without considering how the model was constructed.…”

A review on geometric constraint solving

“…By contrast, the very recent WCM is likely the most promising method to bypass those limitations. Successful applications of this method have been reported, including mechanism design, freeform surface design, (Hu et al, 2017;Mathis & Schreck, 2014;Zou & Feng, 2019bZou et al, 2014), to name a few.…”

Basics of solid CAD system modeling in teaching

“…В англоязычной литературе термины более узконаправлены 1 , однако до сих пор нет четкого соответствия между названием операции на английском и русском языках. Это приводит к проблеме локализации иностранного программного продукта, выражающейся в том, что один и тот же англоязычный термин в разных локализациях переводится по-разному.…”