<title>Mapping gray-scale image to 3D surface scanning data by ray tracing</title>

Abstract

The extraction and location of feature points from range imaging is an important but difficult task in machine vision based measurement systems. There exist some feature points which are not able to be detected from pure geometric characteristics, particularly in those measurement tasks related to the human body. The Loughborough Anthropometric Shadow Scanner (LASS) is a whole body surface scanner based on structured light technique. Certain applications of LASS require accurate location of anthropometric landmarks from the scanned data. This is sometimes impossible from existing raw data because some landmarks do not appear in the scanned data. Identification of these landmarks has to resort to surface texture of the scanned object.Modifications to LASS were made to allow grey-scale images to be captured before or after the object was scanned. Two-dimensional grey-scale image must be mapped to the scanned data to acquire the 3D co-ordinates of a landmark. The method to map 2D images to the scanned data is based on the collinearity conditions and ray-tracing method. If the camera centre and image co-ordinates are known, the corresponding object point must lie on a ray starting from the camera centre and connecting to the image co-ordinate. By intersecting the ray with the scanned surface of the object, the 3D coordinates of a point can be solved. Experimentation has demonstrated the feasibility of the method.