July 20, 1998

Publications by W. Förstner's group, Institut für Photogrammetrie, University of Bonn, Germany:

• Models for Photogrammetric Building Reconstruction, C.Braun et al., Computer & Graphics 1995
• Object-oriented modeling for the extraction of geometry, texture and reflectance from digital images, Müller, H, '98

BibTeX references.

The paper discusses the modeling necessary for recovering man made objects - in this case buildings - in complex scenes from digital imagery. The approach addresses all levels of image analysis for deriving semantically meaningful descriptions of the scene from the image, via the geometrical/physical model of the objects and their counterparts in the image. The central link between raster image and scene are network-like organized aspects of parts of the objects. This is achieved by generically modelling the objects using parametrized volume primitives together with the application specific constraints, which seems to be adequate for many types of buildings. The paper sketches the various interrelationships between the different models and their use for feature extraction, hypothesis generation and verification.

A semi-automatic system for extracting topographic features is being migrated to an object-oriented design for better maintainability. For that purpose an object-oriented model of the extracted objects and the extraction methods is required. Moreover an appropriate software component model for the exchange with other systems is needed. We have modeled a class hierarchy for objects, that can be semi-automatically extracted from digital images. These objects are characterized by geometric, textural and reflectance properties. We have classified the extraction methods and modeled the message transfer of an interactive extraction method. The component technologies CORBA and JavaBeans were used to make the extracted objects and system components available for other systems. We found out that an access to the objects of the Semi-Automatic System by operation calls allows a more flexible data transfer and control of the system than standard file transfer. Therefore Geographic Information Systems (GIS) should support appropriate software component models to co-operate optimally with interactive or semi-automatic feature extraction systems.

Notes :

• Using CORBA, the operations on an object are made available for other objects on different systems.
• RANSAC Technique: RANdom SAmple Consensus is used to determine a best fit of building parameters from a given set of image edges.
• Automatic fine adjustment by robust spatial resection is performed using all line segments in all images. It provides an optimal fit of the selected model to the image data.

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