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FAST OBJECT RECORDING BY MEANS OF STRUCTURED LIGHT AND PHOTOGRAMMETRIC 
TECHNIQUES 
Wolfgang Riechmann 
VOLKSWAGEN AG, Research and Development, 1785-EZLP 
D-38436 Wolfsburg 
Federal Republic of Germany 
Phone: ++49-5361-929532, Fax: ++49-5361-972444 
ABSTRACT 
In the field of industrial optical 3D metrology, rapid and contact-free acquisition of geometric object information 
is becoming ever more important. An active optical triangulation method known as 'Coded Light Approach' which 
is particularly characterised by a rapid and robust measurement of object points can be carried out without 
preparation of the object surfaces. The precision of this method can be improved by the combination with the 
phase shifting technique. Mathematical models of projection and image acquisition, photogrammetric system 
calibration and techniques of highly accurate image measurement are combined. This opens up the possibility 
of making use of the advantages of both techniques, i.e. the high speed of measurement and robustness of 
active systems and the flexibility and precision of photogrammetric methods. 
Theoretical and empirical investigations show a relative precision of 1 : 5000 to 1 : 10000 relative to the 
expanse of the object. Data acquisition for up to 250 000 object points can be carried out in a fraction of a 
second. The subsequent calculation of the 3D coordinates requires a few seconds. 
KEY WORDS: structured light, coded light approach, phase-shift, industrial, 3D 
1. INTRODUCTION 
Both during development and in production, fast acquisition of geometric data is needed not only to measure 
the shape of vehicle models and parts but also to check production tolerances. It is not sufficient merely to 
measure points. Rather the exact recording of a surface by numerous points in critical i.e. curved areas is 
necessary. The results must finally be transformed into the object coordinate system. Today for this 
measurement problem, coordinate measurement machines (CMM's) and gauges are most commonly used. To 
support this, optical 3D metrology can and should be used here. 
In the last 20 years a variety of optical and contact-free methods has been developed, which differ in 
performance and applicability /Tiziani 1993/. Often, industrial surfaces do not show sufficient texture so a kind 
of structure has to be projected. A simple method of industrial surface measurement is the scanning of a surface 
with a laser spot. Having the well known geometry between projection and recording device in view, the surface 
coordinates of a projected laser point are easy to calculate. 
Many methods work with structured light, to project texture information onto the surface. A common method of 
stripe projection is the moiré technique. This technique is based on the superposition of two line grids, each 
with a constant, i.e. not variable grid size. This method is qualified for more or less homogeneous surfaces. In 
the case of structured surfaces the ambiguity of the stripe projection can not be solved. 
IAPRS, Vol. 30, Part 5W1, ISPRS Intercommission Workshop "From Pixels to Sequences”, Zurich, March 22-24 1995