THE ACCURACY OF THE RESEAU-SCANNING CAMERA (RSC) IN COMPARISON WITH THEODOLITE- AND 
PHOTOGRAMMETRIC SYSTEMS 
Wolfgang Riechmann 
Research and Development, Volkswagen AG 
D-3180 Wolfsburg 
Federal Republic of Germany 
Commission V 
ABSTRACT 
High-accuracy optical 3D measurement techniques have been increasingly applied in the quality control of industrial 
assembly tooling. While on-line theodolite systems are used operational there is still a lack of such powerful precise 
photogrammetric systems. 
With the realisation of the RSC a efficient high resolution photogrammetric on-line system is available. In order to 
classify the accuracy of the computer controlled Réseau-Scanning Camera (RSC), a comparison with standard 
measurement tools is carried out. After a short description of the camera-based and theodolite-based systems used, 
the results of a test field measurement are presented. 
Key words: high resolution digital object recording, on-line, comparison of measurement Systems 
1. INTRODUCTION 
In the past, measurements and their evaluation did not 
happen simultaneously. With the introduction of reliable 
electronic reading devices, the requirement arose for 
faster preparation of experimental results. Theodolite 
systems, with their electronically readable graduated 
circles, were the first automated devices in the field of 
geodesy. 
These were soon used in the design of computer- 
controlled theodolite systems. These systems are in 
current use [Kahmen et al. 1984, Gottwald 1987]. The 
development of CCD-sensors made the first steps 
towards on-line applications possible in the field of 
photogrammetry. Besides photogrammetry, other 
disciplines are also attempting to use these sensors to 
reconstruct a three-dimensional object (e.g. robotics, 
machine vision). Precise 3D point determination 
however remained the domain of photogrammetry. The 
limited resolution of CCD-sensors considerably reduces 
the precision attainable in the object space compared to 
analogue film used in classical photogrammetry. While a 
precision of 1:100000 or better is attainable by making 
measurements in the film, object precision of 1:5000 to 
1:10000 can be attained by evaluating digital images 
recorded by CCD-sensors. This assumes a subpixel 
precision of 1/10 to 1/20 of an image element, which is 
relevant for practical applications. 
The development of the Réseau-Scanning camera 
makes it possible to record large image formats 
sequentially in partial digital images, and to perform on- 
line evaluations e.g. measuring image coordinates. 
Furthermore, each partial image can be recorded with 
this camera in a different focus position retaining a 
constant interior orientation. 
A comparison with other on-line and off-line systems 
from photogrammetry and geodesy was performed in 
order to classify this new camera. 
2. A SHORT DESCRIPTION OF MEASUREMENT SYSTEMS 
USED IN THE COMPARISON 
Prerequisite of a precision comparison is all systems 
being able to measure the same signalized points. 
Circular points are preferable for optical measurement 
as their image remains unchanged on rotation and the 
problem ‘point measurement in digital image' is largely 
independent of scale. That means that if circular marks 
are used for comparison, tactile measurement systems, 
e.g. coordinate measurement machines, are unsuitable 
as comparison systems as they cannot trace the edge of 
the circle accurately enough. Bearing this in mind, the 
following brief descriptions of the measurement systems 
used have been included in the comparison.