On-line, collision-free positioning of a scanner during fully automated three-dimensional measurement of cultural heritage objects

摘要

Fully automated three-dimensional (3D) measurement (either with contact or non-contact measurement heads) cannot be easily completed without detailed a priori knowledge of the measured object. This requirement may be easily fulfilled for objects whose CAD models are available (for example, mechanical parts); however, for unique artifacts (such as sculptures), such models are usually unavailable. A description of the object's shape is required to create a list of positions at which the scanning head should be placed to completely measure the whole object (so-called next best views list). For unique objects, this analysis has to be performed on-line during measurements, using obtained data to update the list. For a fully automated measurement, the scanning system must be positioned mechanically, and the transition between subsequent head positions has to be collision free. This paper presents a novel system for 3D digitization of cultural heritage objects which allows one to perform completely automated shape measurements in a given volume with sampling resolutions up to 10 000 points/mm~2. Its main novelties are the next best view module for identifying the best position and orientation of the measurement head in subsequent directional scans (optimized for artifacts of size much bigger than the measurement volume) and flexible software modules for inverse kinematics and collision detection, which allow one to build a positioning system tailored to specific measurement objects. The system is used for digitization of a collection from the Wilanow Palace Museum, Warsaw.