nann, Schwermann 
Photogrammetric 3D-Documentation of the Cathedral of Aachen 
145 
ng hidden lines 
,t one in the outside, 
ng problems occured 
first time a computer based geometrical basis of the cathedral is now available. In order to promote the overall view about the project 
data a special image database has been additionally implemented. This database basically consists of a table with all exposures and 
their orientation parameters. If the user needs some detailed information about the building, he queries the database concerning the 
related photographs and drawing data. Both are then shown at the display using superimposition techniques similar to the normal 
photogrammetric evaluation process (fig. 3) and are available for individual research tasks. 
In addition to the mentioned results some special products have been developed furthermore. In the following some examples are 
pointed out: 
5.1 Surface and volume models 
Primarily the object geometry is represented as a classical wire frame model. The drawings mainly consist of lines and curves. An 
obvious step is the subsequent generation of surfaces from the drawing data. For this lines and curves belonging together are summa 
rized and new surface objects are created. In the simplest case this surface is a plane segment. In general however B-spline-sufaces 
with a threedimensional curvature are established. In most cases the operator first measures the main lines and edges of building 
elements and then he constructs surface and volume elements. Only simple elements are placed directly as volumes during the 
evaluation process with PHIDIAS. Especially the columns carrying the roof have been immediately created even as volume models. 
Figure 5 demonstrates a surface model showing an interior part of the cathedral as an extract. 
; photographs. These 
ems, because the use 
e images, which are 
hould be recorded in 
gain or measured by 
•ge and wide. Hence, 
be kept sufficiently, 
thedral was executed 
: and the photogram- 
CAD drawings. The 
cathedral the follow- 
lot outputs should be 
Figure 5: A surface model of the cathedral (extract) 
5.2 Intersection drawings and hidden line drawings 
After creating surface and volume models the prerequisites for producing intersection or hidden line drawings are given. Intersection 
drawings such as hidden line drawings are predominantly achievable by MicroStation automatically. Figure 6 shows the Hungarian 
chapel as a first example. It should be mentioned that the drawings normally have to be edited by an operator, because automatic 
generation regularly still reveals a lack. The extent of the rework depends on the quality of the surface models. Creating of hidden 
lines is a time consuming process. Due to the large scope of the drawing data of the cathedral the computation took up to several 
hours per project. 
data. Meanwhile the 
e daily work. For the 
Figure 6: The Hungarian Chapel and one of its intersection drawings