locate highly 
>. Stroboscopic 
ı not working 
the motion of 
images. Thus, 
ems for object 
ble to allow the 
to his special 
edings ISPRS 
n Pixels to 
netry & Rem. 
73-149 (Poster 
sis and other 
1-225 (Motion 
A system for 
n: Optical 3-D 
. Gruen and H. 
12 - 21. 
rafie. Schriften- 
it der Bundes- 
cts with digital 
hotogrammetric 
tography and 
Yovements. Int. 
Sensing, Vol. 
| system for the 
uences for 3-D 
'hotogrammetry 
urne, Australia, 
t of structures 
Laser-Tracking- 
t Techniques III 
n) Wichmann, 
996 
  
  
CAD-based Reverse Engineering with Digital Photogrammetry 
Frank Petran 
Peter Krzystek 
INPHO GmbH Stuttgart 
e-mail: inpho@inpho.de 
Peter Bonitz 
ICEM Systems Hannover 
e-mail : peter_bonitz@icem.de 
Commision V, Working Group 3 
Keywords: Reverse engineering, surface reconstruction, still video camera 
Abstract 
Reverse engineering is characterized by the process of creating a CAD model from a digitized physical model. 
CAD models are typically made up of Bezier splines describing the surface of the object. The reasons for choosing a Bezier 
description are the significant reduction of data handled by the computer system and the convenience with which Bezier splines 
can be modified within the CAD system. 
The digitization of models however usually leads to unsorted point clouds or profiles which are used as a reference to generate 
Bezier splines. 
The paper focuses on the generation of ordered point cloud data and profile data with the aid of a photogrammetric measurement 
system and the application of these data in a CAD system. 
1 Introduction 
Modern manufacturing technniques require that the elements 
that make up a product are brought into the computer, for 
instance in the form of mathematical surface descriptions. 
Reverse engineering plays an increasingly important part in 
the process that starts with an initial idea about a product and 
ends with the product itself. 
The term "reverse engineering" has become a buzzword in 
recent time with a variety of different meanings. In general, it 
describes a lot of subprocesses along the line between 
conceptual design and the end product. 
Thus, it touches, for instances the measurement techniques 
involved in the digitization of the physical model as well as the 
surface reconstruction part in which the raw data are described 
With an appropriate mathematical model. 
It is interesting to note, that the term surface reconstruction has 
also a different meaning in the CAD world. It defines solely the 
mathematical description of the object surface. As fas as this 
surface reconstruction part is concerned reverse engineering 
can also be understood as reverse geometric modelling of raw 
data of an object. We focus in our paper on two different 
scenarios. The classical approach is the surface adaption of a 
CAD model to small surface changes of an existing physical 
model. The second one describes the geometric modelling in a 
CAD system starting from scratch without any a-priori 
mathematical description of the object. 
475 
It is possible today to design a product with the aid of powerful 
CAD-systems almost solely in the computer. There are 
however some physical limitations to the computer, especially 
the representation of a three dimensional object on a two 
dimensional screen. In current design processes there is still a 
need for prototypes, because some proportions of a design 
cannot be judged on the computer screen, especially if 
decissions about the planned product are made by people that 
are less experienced in imagining shapes on a flat screen. Thus, 
in general the design process will include or even start off with 
a prototype. During the design process it may also become 
necessary to apply some modifications to the physical model 
instead of the computer based representation. 
The ideal situation would be to keep the situation of the 
product within the CAD-system and its real world prototype as 
much alike as possible. The modifications applied to the design 
within the virtual CAD-world can easily be conveyed into 
reality using a milling machine. The reverse problem is to 
bring the modifications applied to the prototype back into the 
CAD-system. This can be a very time consuming task, 
especially if high point densities are required. 
The paper reports on a digital photogrammetric system 
employing high resolution still video cameras. Such a system 
has the advantage of splitting the recording phase of the model 
and the measurement phase. The recording requires relatively 
little preparation, since it mainly consists of taking images. 
The measurement phase starts once the images have been 
transferred into a computer. It allows the generation of point 
clouds of variable density as well as cross sections along 
predefined planes through the object. The point density is 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B5. Vienna 1996