Landmark registration for reverse design: a case study on footwear rapid prototyping

Abstract

The reverse design is one of the most widely used techniques in the field of rapid prototyping in industry. In this framework, sometimes the real original model is used so as to define the characteristic lines on its computer aided design (CAD) digitized version. These lines could otherwise hardly be drawn on the two-dimensional (2D) image displayed on the computer screen. The problem posed by this technique is that the sampling device uses a different coordinate system, and therefore it is necessary to carry out an initial calibration of the sampling device for the correct positioning of the points on the surface of the original geometry. The problem, known as ‘landmark registration’, is resolved in fields such as medicine or stereoscopic vision using techniques that include the transformation relating two sets of points: the original model and the virtual model. However, the shoe last has an anthropomorphic geometry that has no corners or relevant points, making it difficult to use these techniques with precision. For this reason, current solutions in the shoe industry involve the inclusion of physical marks in the original model that decrease the digitizing quality and distort the original model. This paper presents a ‘landmark registration’ algorithm for rapid prototyping. This algorithm uses only the set of traces obtained by sampling a physical object, and does not require a pre-characterization of relevant points. The algorithm finds the ideal transformation that minimizes the positioning error and prevents the original model from being damaged. The method is applied to real cases of reverse design for the footwear industry.