International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B4. Istanbul 2004 
  
  
are generally topography, buildings, transportation, plant 
cover, infrastructure and other details related to the goal of 
application. 
Actually, the 3D city models are focused on buildings; 
however it may contain roads, green cover, trees etc. 
according to the usage of model. 
The data is most essential component of the 3D city models. 
Therefore, data should be in appropriate form and accuracy. 
If the data was collected as a purpose of generation of the 3D 
model, it will largely be suitable for use. But, when we 
consider using the existing data, the extra editing jobs will be 
inevitable. 
The 3D city models are highly useful for city administration 
however; collecting required data is costly and very hard. 
Therefore, using existing data for model generation is 
cheaper and practical. Especially existing maps produced by 
phogrammetry is much more suitable for 3D city model 
generation (see Figure 1, 2). 
  
  
Figure 2. Perspective view of digital map 
Addition to the maps, orthophotos and rectified image of the 
building facades are used for visualization of the 3D model. 
These images are draped and rendered on surfaces for photo- 
realistic view. 
4. THE DATA PREPARATION 
In this study, 1/1000-scaled digital maps are used. In order to 
reduce the mess, some unnecessary data such as 
administrative boundaries, walls, railways etc. is eliminated 
from the maps. Selected 53 object types are selected and 
used. Some of those objects are as follows: 
e DTM points 
e  Breaklines 
e Sea and lake boundaries 
e Sea ports 
e Buildings 
e Roads 
e Plant cover boundaries 
e Trees and lamps 
After elimination, those data are classified according to its 
type (see Figure 3). For instance all the buildings types such 
as residential building, mosque, factory etc. are classified in 
the same level. This class is used for generation of the solid 
models of the buildings. Some certain classes are constituted 
for all data types. 
  
Figure 3. Buildings 
4.1 Generation of DTM 
In order to generate DTM, related object’s level is used. This 
level contains features and height points, which can define 
the topography of the area. These features are DTM points, 
declivities, contour lines, boundaries etc. All these features 
are converted to the points. Finally terrain was triangulated 
with these points. But some of these points have wrong z 
values and needs to be eliminated. During the production of 
the maps, human made mistakes causes this wrong z values. 
Sometimes operator can measure the heights incorrectly. 
Therefore these values should be edited or deleted from the 
data during the process. 
In order to correct them, manual or automatic procedures can 
be applied. In manual way, this problem is solved interactive 
control and editing (Yastikli, 2002). Operator triangulates the 
surface and examines the triangles visually. But this method 
causes neglect of the lower errors and time consuming. 
Automatic methods are editing the points automatically with 
selected parameters (Yastikli, 2002). But using this method 
can cause loosing the small details on the surface. In this 
project both of these methods are used for best result. Thus, 
height errors and faulty triangles are corrected or deleted in 
order to reach the precise DTM (see Figure 4). Triangulated 
  
  
  
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