Interrogating witnesses for geometric constraint solving

  • Authors:
  • Sebti Foufou;Dominique Michelucci

  • Affiliations:
  • CSE dept, CENG, Qatar University, PO Box 2317, Doha, Qatar and Le2i, CNRS 5158, Université de Bourgogne, BP 47870, 21078 Dijon, France;Le2i, CNRS 5158, Université de Bourgogne, BP 47870, 21078 Dijon, France

  • Venue:
  • Information and Computation
  • Year:
  • 2012

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Abstract

Classically, geometric constraint solvers use graph-based methods to decompose systems of geometric constraints. These methods have intrinsic limitations, which the witness method overcomes; a witness is a solution of a variant of the system. This paper details the computation of a basis of the vector space of free infinitesimal motions of a typical witness, and explains how to use this basis to interrogate the witness for dependence detection. The paper shows that the witness method detects all kinds of dependences: structural dependences already detectable by graph-based methods, but also non-structural dependences, due to known or unknown geometric theorems, which are undetectable by graph-based methods. It also discusses how to decide about the rigidity of a witness and how to decompose it.