Compared with two-dimensional datasets we have 
to keep in mind that a fully three-dimensional CAD 
model shall be visulized by means of perspective 
projections. The visible part of the object is now 
situated within a viewing frustum, which may widely 
open onto the horizon, if large citiy-areas are 
rendered. 
This means, that in addition to the  GIS- 
recommendations we need strategies to visualize 
the digital data under the conditions of 
perspective projections (cf. Fig 3). 
  
Fig. 3: Perspective view of a digital model of a larger part of 
Vienna (2 km by 2 km) 
Including the texture data of buildings, objects and 
ground surface of the digital model we have to 
manage a total data set of several hundred 
Gigabytes. This large amount of data has to be 
referenced and indexed by a standard data 
manager such as an existing data base 
management system. In line with [Kofler et al. 
1996] we favor the concept of OODB's, where 
efficient queries, transaction support and 
communication tools exist and the novel situation 
of three-dimensional objects and their spatial 
relationships have to be denoted. 
In addition a Level of Detail (LoD) concept has to 
be implemented, which allows the visualization of 
parts of a scene in a rather cost-effective 
manner, according to the perspective enlargement 
of the specific object. 
Part 3. Communications Technology 
Based on the data management system, we grow 
the concept of a geo server for local and remote 
accsess for clients and users with widely available 
3D data for added value services. Data will be 
accessed either as end user’ elaborate products 
or as raw data are required for further processing. 
These two kinds of data processing will require a 
flexible broadband transport technology such as 
currently provided by the upcomming 
Asyncronous Transfer Mode / ATM. 
This provides users both with connection oriented 
services and with the flexibility of a packed 
switched service. So the need for variable 
bandwith will be covered as well as the need for 
high transmission rates up to 622 Mbit/sec. 
End user applications require a common front end 
that will present available data and processing 
tools with a friendly and easy to learn graphic 
interface. In this context we recognise, that 
Hypermedia servers are a global trend and bring 
up standardized and transparent access to the 
data. On top of this existing framework we need 
only to implement specific extensions. 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B3. Vienna 1996 
Results 
The result of our analysis is a work breakdown 
structure which points the different tasks of a total 
procedure for modelling 3D Cityscapes. We know 
from the current literature, that parts of this work 
are investigated and results are presented 
continuously, e.g. the creation of 3D CAD models 
of buildings. Other parts are developed not as well 
as one would wish. This concerns mainly the 
aquisition of source data for the texture of 
facades, the processing of photo-texture and the 
developement of databank-systems to maintain 
and distribute the data of a full-fledged CyberCity 
data set. 
The synopsis of the workflow leads to a work 
breakdown structure. In Table 1 we present a list 
and refer to the computer environment, which is 
needed to perform a specific task . 
  
Table 1 : Elements and equipment for the creation and use of 
3D city models (CyberCities) 
   
  
the 
ant