Refraction effect analysis of using a hand-held laser scanner with glass support for 3D anthropometric measurement of the hand: A theoretical study

Three-dimensional (3D) anthropometric measurement provides much more surface information for ergonomic product design and safety considerations than traditional parameter measurement approaches such as using a caliper. However, some challenges remain for 3D measurement, such as measurement uncertainty introduced by shadow areas and involuntary movement of the body. For 3D anthropometric hand measurement with a laser scanner, the problems are more significant. The traveling laser light is prone to be blocked by the fingers due to the structure of the hand. Additionally, the palm and/or fingers are difficult to hold still without a support, even for a few seconds. In a previous study, a method was proposed for using a handheld portable laser scanner with a glass support. However, during scanning, the spatial relationship between the laser scanner and supporting glass could have a large range of variance, which would increase the uncertainty of the glass refraction errors. In this paper, the general principle of laser scanning through glass is discussed in detail through a ray tracing method. It is found that in most cases no virtual images exist. Then a concept of ‘deduced virtual image’ is put forward and four strategies to calculate coordinates of a measured point are discussed. These strategies are compatible with scanning without through glass in calculating coordinates of a measured point.