Proceedings 18 th International Symposium CIPA 2001 
Potsdam (Germany), September 18 - 21, 2001 
THE POTENTIAL OF NON-CONTACT CLOSE RANGE LASER SCANNERS 
FOR CULTURAL HERITAGE RECORDING 
Wolfgang Boehler (l) , Guido Heinz <2) , Andreas Marbs (1) 
(l) i3mainz, Institute for Spatial Information and Surveying Technology, FH Mainz, University of Applied Sciences, 
Holzstrasse 36, 55116 Mainz, Germany, 
i3mainz@geoinform.fh-mainz.de 
<2) Roemisch-Germanisches Zentralmuseum, Emst-Ludwig-Platz 2, 55116 Mainz, Germany 
KEY WORDS: Laser Scanners, Close Range, Cultural Heritage Recording 
ABSTRACT 
The use of laser scanning methods for the close range measurement of fixed objects has recently become popular in the design and 
manufacture of automobiles, and in body scanning. Laser scanning instruments, mainly developed for such industrial applications, 
are also suitable for cultural heritage recording. The two basic types currently available are ranging lasers and triangulation-based 
devices. With the latter, a light projection is imaged by a CCD camera at a fixed distance. A triangulation type of scanner (MENSI 
S01SIC™ LD with 3Dipsos software) is described, the results of scanning trials are reported and various complexities are pointed 
out. Objects recorded include a statue, a sculptural arrangement, an unearthed Roman boat and architectural facades. We conclude 
that laser scanning is a valuable new method for cultural heritage recording and one which will complement, and, in certain 
applications, replace currently existing methods. 
1. 3D SCANNING 
1.1 Principles of Operation 
3D scanners record three-dimensional coordinates of numerous points on an object surface in a relatively short period of time. To 
accomplish this, a laser beam is projected onto the object surface. The scanning effect is achieved using one to two mirrors which 
allow changes of the deflection angle in small increments. In addition, the entire instrument and/or the object may be rotated to 
achieve a complete 3-dimensional point coverage. High-accuracy recording of angular settlings is important, since the angles 
together with the distance measurements determine the reflecting point position. 
Two different principles for distance measurement are in use: Ranging lasers using the “time-of-flight” principle and instruments 
using CCD cameras where distance measurement is based on the principle of “triangulation”. 
Time-of-FIight 
The so-called “time-of-flight” or “ranging” scanners have a laser diode that sends a pulsed laser beam to the scanned object. The 
pulse is diffusely reflected by the surface and part of the light returns to the receiver. The time that light needs to travel from the laser 
diode to the object surface and back is measured and the distance to the object calculated using an assumed speed of light. (Fig. 1). 
Ranging scanners are able to measure much longer distances than instruments that work by triangulation. They are, however, less 
accurate and especially so at close range. The accuracy is between some millimeters and two or three centimeters, depending to some 
extent on the distance between the object and the scanner (object distance). 
Triangulation 
The second group of scanners is based on a simple triangulation principle. A light spot or stripe is projected onto an object surface 
and the position of the spot on the object is recorded by one or more CCD cameras. The angle of the light beam leaving the scanner is 
internally recorded and the fixed base length between laser source and camera is known from calibration. The distance from the 
object to the instrument is geometrically determined from the recorded angle and base length (Fig. 2). This type of scanner reaches 
3D point standard deviations of less than one millimeter at very close range (less than 2 meters) The accuracy depends on both the 
length of the scanner base and the object distance. With a fixed base length, the standard deviation of the distance measurement will 
increase in proportion to the square of the distance. 
Image matching 
If two cameras are used at the end of a base, image-matching techniques can be used to compute 3D coordinates of large numbers of 
object surface points. If the object is close and lacks detail, a pattern projector can give the necessary texture. These techniques, well 
established in photogrammetry, are not included in this paper, although they should always be considered for recording tasks similar 
to those described below.