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An already established system for surface measurement works with the projection of random patterns. The 
surface coordinates are computed by an automatic evaluation of stereo images by means of correlation 
techniques /Claus 1988/. While the established method works with analogue film, the further developed system 
uses high resolution digital sensors for object recording /Kludas 1995/. 
Another possibility of a reliable and flexible method is the use of structured light by projecting a regular dot grid 
onto a surface. By using the epipolar geometry, the evaluation can be largely automated /Maas 1992/. 
Zumbrunn describes an digital phase measurement, which gets a theoretical accuracy of 1x10'4 /Zumbrunn 
1987/. 
The presented coded light approach (CLA) is a robust and fast measurement technique, which gives a high 
object resolution. For purposes of recording and evaluating simple hardware and fast algorithms can be used. 
As an active triangulation technique, CLA offers the possibility of fast range data acquisition over the entire 
surface. The fundamental measurement principle was proposed in 1979 by Altschuler et al. /ALTSCHULER 1979/. 
Independent of each other, Wahl /WAHL 1984/ and Inokuchi et al. /INOKUCHI 1984/ took it up and developed it 
further. More recently further papers and application reports have been published by different authors. /MALz 
1989, Lay 1992, STAHS, WAHL 1992, BREUCKMANN 1994, MASSEN 1994/. The measurement accuracy given to 
date is restricted in the range of 1:100 - 1:2000 in relation to the object dimension. While this is sufficient for 
some applications in the field of automation and quality assurance (object recognition, completeness check 
etc.), with regard to actual measurement problems (check on tolerances, conversion of real surface coordinates 
into B-spline CAD-models etc.) the requirements are higher. 
With the view to these requirements, VOLKSWAGEN AG R&D Division has taken this technique a step further and 
combined it with the phase-shift method /STRUTZ 1993/. 
2. CODED LIGHT APPROACH AND PHASE-SHIFTING 
In geodesy triangulation is the oldest method for measuring a range of remote points. In an industrial environ- 
ment this principle is realised and implemented e.g. in the form of laser scanners. A laser beam can be spread 
by passing it through a cylindrical lens, which results in a plain of light. Contour sensors use this principle of a 
light stripe and are in operational use in the 
automotive industry. If one picture is necessary to 
record each. laser point or light stripe, the number Projector 
of pictures required can be reduced to Ho 
approximately 8 by the projection of a coded 
binary pattern. 
The Coded Light Approach (CLA) is based on a 
time-space encoding of the measurement area. It 
is realised by projecting a sequence of n Gray- 
coded stripe patterns into the object space (Fig. 1). 
The pattern allows a distinction between 20 
different projection directions (px). Each direction 
is described uniquely by a binary sequence i.e. by 
a n-bit code. 
For the 3D measurement of the object space, 
patterns are recorded by a camera which is 
positioned apart from the projecting device (Fig. 1). : 
The patterns are generated by means of a computer- Object 
controlled transparent LCD and appear deformed on 
the object. In the grey level images recorded by the 
CCD camera, the illuminated and not illuminated 
areas can be divided using a suitable binarizing Fig. 1 Time-space encoding of the object area 
algorithm. The resulting binary images are stored as f by means of stripe patterns /Strutz 1993/ 
  
IAPRS, Vol. 30, Part 5W1, ISPRS Intercommission Workshop "From Pixels to Sequences", Zurich, March 22-24 1995 
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