Abstract— Laser triangulation systems allow for non-contact, accurate and fast digitizing of surfaces. The quality of the digitized surface depends on many factors. Some, like laser emission wavelength, are characteristics of the system. Other factors, like part surface quality are external to the system. Laser triangulation systems project a laser beam onto the surface of the workpiece, so that an image of this projection is captured in a photo-sensor. This image is processed using triangulation techniques to calculate the spatial position of every point on the projection. The sensor does not only capture the light projected by the laser, but also captures the ambient light emitted in the same wavelength of the laser beam. Since calculation of points positions depends on the image characteristics, ambient light becomes a potential error source. The present work evaluates the influence of ambient light on the results of the scanning process. A methodology for testing different light sources under the same digitizing conditions has been developed. Three different criteria have been used to analyze the quality of the point cloud: the number of captured points, the average dispersion of the test point cloud with respect to a reference point cloud, and the distribution of such geometric dispersion across the whole surface. Index Terms— Laser triangulation, digitizing, influence of ambient light. I. INTRODUCTION Laser triangulation (LT) systems are used for inspection and reverse engineering of surfaces. Their characteristics make them suitable when accurate and fast non-contact scanning is needed. In most LT systems, the projection of a laser beam onto a surface is captured as an image in a charged coupled device (CCD). Applying image processing techniques and the triangulation principle, 3D coordinates of the surface points are acquired (Fig.1). If the distance between a particular point P and the CCD matches exactly the value of the reference distance (stand-off), its image in the CCD will be placed exactly in a reference point P’. Otherwise, if the point onto Manuscript received March 18, 2008. This work is part of the results obtained in a research project supported by the Spanish Education and Science Ministry (MEC-04-DPI2004-03517) and FEDER. D. Blanco is Lecturer of the Manufacturing Engineering Department in the University of Oviedo, Campus of Gijón, Spain (phone: 985-182-444; fax: 985-182-016; e-mail author: dbf@uniovi.es ). E. Cuesta and C.M. Suárez are Senior Lecturers of the Manufacturing Engineering Department in the University of Oviedo, Campus of Gijón, Spain (phone: 985-182-016; fax: 985-182-016; e-mail authors: ecuesta@uniovi.es ; csuarez@uniovi.es ). P. Fernández has collaborated with the Manufacturing Engineering Department in the University of Oviedo for developing the research project mentioned above (e-mail author: pedrofa@uniovi.es ) the surface were further away a distance H in the direction of the laser beam, its image on the CCD will be placed a distance h from the reference point. As the geometry of the laser system is completely known, it is possible to determine the spatial position of every single point from its image position on the sensor [1]. In order to digitize a part, a relative movement between the laser system and the part surface is needed, so that the laser beam projection sweeps the target surface. This results on a set of digitized points (point cloud) that represents the surface of the part. Usually, LT systems are installed on a coordinate measured machine (CMM) that provides precise and controlled displacements along its axes. Using motorized heads on the CMM also allows for rotating the LT system to obtain a suitable orientation for the scanning process. Accurate calculation of the spatial position for each point of the laser stripe depends on the accurate calculation of the centroid of its light distribution in the sensor [1], [2]. If the intensity of the light distribution captured in the sensor is too weak, the system can not properly calculate the position of the points. Otherwise, if laser intensity is too high, the sensor will turn into saturation, so that the system could not calculate the position of points. For intermediate situations, the light distribution is analysed to determine its centroid position, which corresponds to distance h measured from reference point. Consequently, the light distribution affects the accuracy of distance H calculation (Fig.1). Lens Laser Diode CCD Sensor Reference Distance (Stand off) P’ P +H ‐H ‐h +h Fig. 1. Scheme of the laser triangulation principle Influence of Ambient Light on the Quality of Laser Digitized Surfaces D. Blanco, P. Fernández, E. Cuesta and C. M. Suárez Proceedings of the World Congress on Engineering 2008 Vol I WCE 2008, July 2 - 4, 2008, London, U.K. ISBN:978-988-98671-9-5 WCE 2008