22nd CIPA Symposium, October 11-15, 2009, Kyoto, Japan LOW COST SOLUTIONS FOR DENSE POINT CLOUDS OF SMALL OBJECTS: PHOTOMODELER SCANNER VS. DAVID LASERSCANNER E. Alby a,* , E. Smigiel a , P.Assali a ,P.Grussenmeyer a , I.Kauffmann-Smigiel b a Photogrammetry and Geomatics Group MAP-PAGE UMR 694, Graduate School of Science and Technology (INSA), 24 Boulevard de la Victoire, 67084 STRASBOURG, France. (emmanuel.alby, eddie.smigiel, pierre.assali, pierre.grussenmeyer)@insa-strasbourg.fr b Etude des Civilisations de l'Antiquité, CNRS - Université de Strasbourg UMR 7044 5 allée du Gal Rouvillois, CS 50008, 67083 Strasbourg, France isabelle.smigiel@etumb.u-strasbg.fr KEYWORDS: cultural heritage, documentation, acquisition, triangulation-based laser, photogrammetry, comparison ABSTRACT: The study of archaeological artifacts requires a great care for the object. Current technologies allow the study of the object scanned in three dimensions. Hence, the digitization of objects has almost become compulsory for simplicity of study and analysis. For each scale of objects, dedicated hardware equipments exist oftentimes at important costs. Among others, scanning arms, handheld scanners, triangulation scanners, terrestrial laser scanners offer a wide variety of possibilities to produce 3D data. However, the question of cost is central in the field of archaeological research. That is probably why the technology is not widely spread in the community. Besides, the question of knowhow is also an important issue. Despite the appearances, a 3D digitization project is not so easy to carry out. Hence a low cost solution susceptible of being operated with reasonable effort could contribute to popularize 3D acquisition tools. In our study, we focus particularly on two solutions: David Laserscanner and PhotoModeler Scanner. Both systems come from two different techniques: laser scanning and photogrammetry. They can both produce dense clouds of points of small objects. Our comparison is completed according to several criteria. The most important criterion is undoubtedly accuracy; it is therefore significant to quantify the ability to produce a reliable point cloud. To compare the point clouds obtained with both systems, we use a point cloud provided by an arm scanner whose accuracy is less than 1/10th of a millimeter. As a second important criterion the maximum spatial resolution reachable for a specified hardware configuration is obtained by the optimization of the acquisition parameters. Acquisition is often repetitive and on site. Ergonomics of systems is also important to evaluate. The interface can be divided into two parts: hardware and software. It is the combination of the two phases of acquisition and processing which will take into account of the general ergonomics of the systems. 1. INTRODUCTION 3D modeling has been a subject of intensive research for a long time. Mature solutions exist and improvements of their performances have been appearing constantly. In the field of cultural heritage and among others, in archaeology (Forte & Pietroni, 2009; Guidi et al., 2004; Papagiannakis et al., 2005), these technologies have been used successfully for many years. Applications in documentation, representation, preservation and reconstruction should convince if necessary the huge possibilities of 3D digitizing. However, though many impressive results may be found in the literature, 3D modeling remains a sophisticated task which requires specific skills as well as adapted equipment (Al-kheder et al., 2009). Hence, though popular and well known, the technology has not spread overall and many archaeologists, though interested, may be discouraged to get introduced in this world. Thus, the need for affordable solutions still exists. In this paper, two low-cost solutions are presented: dense point cloud photogrammetry (through the PhotoModeler Scanner © , EOS Systems © , PMS) and the DavidScanner Laser, DSL. Instead of presenting the theoretical aspects of both methods, which is of little concern for practitioner, a case study is carried out through the very beginning till the final digital model. The stress is put on the ergonomics of the method and the minimum skills are presented so as to convince the reader that, provided he is willing to invest a little time, he will be able to obtain results with a very good precision. The performances of the two methods are hence presented in terms of accuracy. The paper ends with a comparison (advantages / drawbacks) of the two methods to serve as a guide for whoever may be interested in trying 3D modeling. 2. SCANNER AND PHOTO TECHNOLOGIES 2.1. David laserscanner DSL belongs to the so-called triangulation-based laser range finders. A complete description of the system may be found in (Winkelbach et al., 2006). The principle is as follows: The laser ray is expanded to a plane by a cylindrical lens. The image of the intersection of this plane with a known background allows determining the laser plane’s equation. Then, the image of the intersection of the laser plane and the surface to digitize allow determining the xyz co-ordinates of a set of points.