-9 
3D SCANNING INSTRUMENTS 
Wolfgang BOEHLER, Andreas MARBS 
i3mainz, Institute for Spatial Information and Surveying Technology, FH Mainz, University of Applied Sciences, 
Holzstrasse 36, 55116 Mainz, Germany, 
i3mainz@geoinform.fh-mainz.de 
KEY WORDS: 3D, scanner, close range, cultural heritage. 
ABSTRACT: 
All instruments collecting 3D coordinates of a given region of an object surface automatically and in a systematic pattern at high 
rates and achieving these results in near real time are considered as 3D scanning instruments in this article. For cultural heritage 
documentation, mobile systems for close- and mid-range applications are applicable. Different technical solutions have been 
developed to obtain the necessary measurements for the derivation of the 3D point coordinates on a reflecting surface. Ranging 
scanners measure horizontal and vertical angles and compute the distance either by the time-of-flight method or by comparing the 
phases of the transmitted and received wave form of a modulated signal. Triangulation type instruments include a base. They 
analyze the location of a projected laser spot or other pattern using one or two CCD cameras. The different principles lead to a 
different accuracy behavior of the distance measurement. Since noisy measurements are difficult to process, a high accuracy of the 
scanner is desirable. This leads to the conclusion that no single scanner can fulfil all demands in different cultural heritage recording 
projects. 
Besides accuracy considerations, other characteristics are important for the selection of the most suitable instrument for a certain 
task. Among these are scanning speed and resolution, range limits, influence of interfering radiation, possible field of view, inclusion 
of imaging cameras, ease of transportation, type of power supply, and the quality of the scanning software. 
A list of presently available 3D scanners completes the overview given in this article. 
1. DEFINITION 
To the knowledge of the authors there is no generally accepted 
definition concerning instruments which are considered to be 
3D scanners. Since different technical principles are used to 
measure the elements needed to compute 3D coordinates, some 
technicians have tried to delimitate 3D scanners from other 
instruments based on their technical way of operation. Among 
other drawbacks, this has also led to a superfluous discussion 
whether 3D scanning ‘belongs’ to geodetic surveying or to 
photogrammetry. 
For the user, however, it is the result only that counts, 
regardless of the method used to achieve it. From a user’s point 
of view, a 3D scanner is any device that collects 3D coordinates 
of a given region of an object surface 
• automatically and in a systematic pattern 
• at a high rate (hundreds or thousands of points per second) 
• achieving the results (i.e. 3D coordinates) in (near) real 
time. 
The scanner may or may not deliver reflectivity values for the 
scanned surface elements in addition to the 3D coordinates. 
3D scanners are used 
• stationary in a fixed position (e.g. in production lines for 
quality control) 
• as mobile systems on tripods or similar stands for close 
and mid-range applications 
• as airborne systems for topographic applications. 
2. USE IN CULTURAL HERITAGE 
DOCUMENTATION 
Metric cultural heritage documentation tasks usually comprise 
close range recording applications. Objects range from small 
artifacts over sculptures to buildings. Irregular shapes and 
surfaces are encountered frequently. Often, the time available 
for the measurements is limited. In the past, close range 
photogrammetry was the only method to meet these demands. 
3. PRINCIPLES OF OPERATION 
3.1 Ranging scanners 
Time of flight of a laser pulse. A laser pulse is sent to the 
object and the distance between transmitter and reflecting 
surface is computed from the travel time between signal 
transmission and reception (fig.l). This principle is well known 
from electronic tacheometers. In fact, a tacheometer with 
motor-driven axes could be programmed to work as a scanning 
device. Measuring rates would be very low, however, since - 
due to the mass of the instrument - the incremental rotation 
steps around the axes cannot be performed fast enough, signal 
processing usually takes too long and angular values have to be 
read troublesome from coded circles. Scanners use small 
rotating devices for the angular deflection of the laser beam (at 
least for one of the two angles) and use simpler algorithms for 
range computation which may lead to poorer accuracy values. 
Typical standard deviations of range measurements by time-of- 
flight scanners are in the order of some millimeters. Since 
ranges are relatively short, this accuracy is nearly the same for 
the whole object space. The 3D accuracy is also influenced by 
the accuracy of the angular pointing of the beam. Few investi 
gations concerning this matter have been made public yet. 
Phase comparison method. This method is also well known 
from tacheometric instruments. In this case, the transmitted 
beam is modulated by a harmonic wave and the distance is 
calculated using the phase difference between transmitted and 
received wave. From the users point of view, the method is not 
very different from the time-of-flight method. Due to the more