ree 
lon 
les 
ind 
ital 
fa 
t is 
In 
  
  
Ermes, Pierre 
CONSTRAINTS IN CAD MODELS FOR REVERSE ENGINEERING USING 
PHOTOGRAMMETRY 
Pierre ERMES 
Delft University of Technology, The Netherlands 
Faculty of Civil Engineering and Geosciences, Department of Geodesy 
p.ermes@geo.tudelft.nl 
Working Group V/2 
KEY WORDS: CAD, Modeling, Photogrammetry, Reconstruction 
ABSTRACT 
The paper discusses the use of geometric constraints in a CAD model-based photogrammetric system. The CAD models 
are represented by CSG (Constructive Solid Geometry) models. The geometric primitives that make up the CSG model 
are parameterized by their pose and shape parameters. Geometric relations, or constraints, between these primitives are 
expressed using these parameters. 
Constraints can be applied both between the geometric primitives in a CSG model and between CSG models. For 
example, continuity requirements between two connected piping elements constrain the relative position of the elements 
as well as their relative orientation. 
The constraints are formulated as weighted linearized observation equations and are included in a least-squares 
adjustment together with the photogrammetric measurements on the edges. The exterior orientation parameters of the 
images are also estimated in the adjustment. 
A pilot project was done on a gas-exploration site. Only the images and a couple of tape measurements were acquired 
on the site - no markers were used. The model-oriented photogrammetric system, Piper, combines image observation 
and geometric constraints in a bundle adjustment to reconstruct an accurate CAD model of the installation. 
1 INTRODUCTION 
An accurate "as-built" model of a piping installation can serve several purposes; such as revamping, inspection and 
maintenance, and part replacement. Safety regulations may also demand that an up-to-date model of an installation is 
available. Photogrammetry is an often used technique for the reconstruction of industrial installations (Benning, 1997), 
(Hilgers et al., 1998), (Jones et al., 1996). 
Industrial installations are usually built with standardized components for economic reasons. CAD models of these 
components are available in large databases or catalogs. It appears that most standardized components can be modeled 
with only a few geometric primitives using Constructive Solid Geometry (CSG). 
We have developed a model-oriented photogrammetric system for generic CSG models that exploits this 
standardization by providing a catalog from which the operator can select a specific model that he/she wants to 
measure. The system also comprises an interactive measurement method for parameterized CSG models, a semi- 
automatic fitting procedure to increase the measurement precision, and a bundle adjustment for the simultaneous 
estimation of the CSG parameters and the image exterior orientations. Known geometric relations within CSG models 
and between CSG models can be taken into account by introducing geometric constraints. 
This paper focusses on the use of geometric constraints with CSG models in a photogrammetric system. The next 
section discusses constraints in CAD applications compared to constraints in photogrammetric applications and 
motivates the choice of the mathematical model. Section 3 gives a general overview of our model-oriented 
measurement system, while Section 4 introduces frequently used geometric constraints within an industrial installation. 
Section 5 explains how the exterior orientations of the images are determined in our set of test data, which is discussed 
in Section 6. Finally, Section 7 concludes. 
  
International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B5. Amsterdam 2000. 215