Recent years, the safety of high scaffold has become the focus of construction site, and one of the most important problems is the geometrical stability.
近年来高型脚手架的安全成为建筑工地使用的焦点，其中最重要的一个问题就是脚手架的几何不变条件。
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In this paper, we first focus on the CAD-based object model construction and then introduce a rule-based method to precompile this geometrical model into a match tree for 3-d object orientation.