The efficient generation of data for 3-D city models and their handling in Spatial Information Systems has become feasible. The derivation of this data from aerial and terrestrial images with semi-automated techniques constitutes the most powerful tool currently available to fulfill this task. Semi-automated object extraction has become a viable concept for the generation of 3-D city models. CyberCity-Modeler (CCM) has been developed with the aim of creating not only buildings, but also other objects pertaining to a city model efficiently and with a high degree of flexibility concerning the level of detail. In its commercial implementation, CCM has been confronted with a number of user requirements which needed to be observed. This led to some extensions in functionality, which are addressed in this speech: Geometrical regularization of buildings, editing functions for topology adjustment, integration of facades and other vertical walls and modeling of overhanging roofs. These extensions of the original concept make CyberCity-Modeler an even more powerful tool for 3-D city modeling.

(Visualization left with CyberWalk, right with TerrainView)
Introduction
CyberCity-Modeler (CCM) represents a methodology for semi-automated object extraction and modeling of built-up environments from images of satellite, aerial and terrestrial platforms. It is generic in the sense that it allows to model not only buildings, but all objects of interest which can be represented as polyhedral model, which includes DTM, roads, waterways, parking lots, bridges, trees, ships and so forth. As such it produces 3-D city models efficiently, with a high degree of flexibility with respect to metric accuracy, modeling resolution (level of detail), type of objects and processing speed.

CCM is a commercial software product, marketed by the ETHZ spin-off company CyberCity AG (www.cybercity.tv). As a matter of fact, there is a steadily increasing interest for 3-D city models, with the current major customers being city planning and surveying offices, industrial facilities (chemical and car industry) and telecom companies. With the different types of customers comes a great variability in project specifications. Here it turned out to be of advantage that CCM was set up from the very beginning as a technique with high degree of flexibility. In spite of that, some additions had to be developed to extend of the original functionality in order to fulfill specific requests.

This paper reports about these extensions. After a brief review of the original CCM concept we will address the issues of regularization of buildings, editing functions and the integration of building facades, automated modeling of roof overhanging roofs as well as mapping wall textures.

CCM – the concept
CyberCity-Modeler, was designed as a tool for data acquisition and structuring for 3-D city model generation. From the very beginning, CCM has been devised as a semi-automated procedure. This was done in view of the need to observe the following constraints:

• Extract buildings, and other objects like traffic network, water, terrain, vegetation.
• Generate truly 3-D geometry and topology.
• Integrate natural (real) image textures.
• Allow for object attributation.
• Keep level of detail flexible. Accept virtually any image scale.
• Allow for a variety of accuracy levels (10 cm to 2 m).
• Produce structured data, compatible with major CAD and visualization software.

In site recording and modeling, the tasks to be performed may be classified according to:

• Measurement.
• Structuring of data.
• Visualization, simulation, animation.
• Analysis.