UTILIZATION OF CAD MODELS FOR THE OBJECT ORIENTED 
MEASUREMENT OF INDUSTRIAL AND ARCHITECTURAL OBJECTS 
Andre Streilein 
Institute of Geodesy and Photogrammetry 
Swiss Federal Institute of Technology 
CH-8093 Zurich, Switzerland 
e-mail: andre ? geod.ethz.ch 
Commission V, Working Group 3 
KEY WORDS: CAD, digital close-range photogrammetry, model based analysis, object oriented measurement. 
ABSTRACT 
An object oriented measurement approach using CAD models for the initialization of an automatic measurement process 
and for the verification of the measurement results is presented. CAD models are used in an a priori and a posteriori 
mode. The human operator assigns responsibility for the image understanding part (high level grouping), and the 
computer for the actual measurement and the data handling. The performance and results of this measurement approach 
is demonstrated on an architectural object. 
KURZFASSUNG 
Eine objekt-orientierte Messmethode, die auf der Grundlage eines CAD-Models eine automatische Messroutine auslóst 
und deren Resultate überprüft, wird vorgestellt. Dabei werden CAD Modelle sowohl im a priori als auch im a posteriori 
Modus angewendet. Der Operateur zeichnet für die Bildinterpretation verantwortlich, während der Computer für die 
aktuellen Messungen und die Verwaltung der Daten zuständig ist. Vorgehensweise und Resultate dieser Methode werden 
am Beispiel eines Architekturobjektes dargestellt. 
1. INTRODUCTION chitecture (Saint-Aubain, 1990; Stevens and McKay, 
: : : ; 1990; Kempa and Schlüter, 1992; Albertz and Wiede- 
This paper describes an object oriented measurement AP" mann, 1995), in the field of heritage recording (Robson, et 
proach using CAD models for the initialization of an auto- „1 1994: Sawyer and Bell, 1994), in the field of city mod- 
matic measurement process and for the verification of the eli (Lang and Schickler 1993: Gruber et al 1995: Mason 
measurement results. This measurement approach is em- ang Streilein, 1996), or in the field of industrial applica- 
bedded in the software environment DIPAD, currently un- tions (Oshima, 1992; Chandler, Still, 1994; Chapman, et 
der development at ETH Zurich. al., 1994). Examples can be found even for the design of 
DIPAD combines digital photogrammetric methods with ~~ close-range photogrammetric networks (Mason, 1994). 
the capabilities of a CAD system. CAD models are used 
in an a priori and a posteriori mode. The overruling princi- 
ple is, that the human operator assigns responsibility for 
the image understanding part (high level grouping), and 
the computer for the actual measurement and the data han- 
dling. The user indicates relevant parts of the object in the 
CAD environment by approximating a geometric topolo- 
gy to 1t. The photogrammetric algorithm matches this to- there are systems, who accept or require CAD information 
pology with the mage data of multiple Images, iteratively prior the measurement process (e.g. the systems described 
refines the coarse object model that is given and transfers — :, by El-Hakim and Pizzi (1993) or Schickler (1992). 
the final result back to the CAD environment, including 
information about precision and reliability of the result. Object models can be treated as abstractions of real world 
objects. The most important role played in model 
definition is the proper balance between correctness and 
tractability, i.e., the results given by the model must be 
adequate both in terms of the solution attained and the 
cost to attain the solution. 
Different software packages employ CAD models. Some 
of which are addressed in (Fellbaum, 1992), where an 
overview of low-cost photogrammetric systems using 
CAD is given and in (McGlone, 1995) where an overview 
of various systems in computer vision using CAD models 
is given. Most systems use CAD models exclusively for 
the representation of photogrammetric results. However, 
In Sect. 2 the ability of CAD systems for the representa- 
tion and structuring of 3D data is discussed. Sect. 3 gives 
an overview of the modelling and measurement principles 
of DIPAD. And finally in Sect. 4 results of this measure- 
ment approach will be demonstrated on an architectural 
object, the Otto-Wagner-Pavillon in Vienna). The information usually conveyed in any CAD applica- 
tion is geometry, and the most common way of introduc- 
2. MODEL REPRESENTATION AND DATA ing geometry is by using the concept of building blocks. 
STRUCTURES OF CAD Every object maybe decomposed into a small number of 
geometric pieces or graphic primitives. Basic graphic 
For the representation of three-dimensional data CAD primitives, e.g. points or dots, straight lines, polylines, 
models have been used widely in photogrammetric appli- filled areas, exist both in 2D and 3D environments. In ad- 
cations. Various examples can be found in the field of ar- — dition there are advanced primitives in 2D, e.g. circles, 
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International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B5. Vienna 1996 
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