Abstract



3D GIS Data Acquisition Using VISAT - A Mobile Mapping System

Dr. Naser El-Sheimy
Professor and Canada Research Chair
Department of Geomatics Engineering, The University of Calgary
Alberta, Canada
Email: naser@geomatics.ucalgary.ca


Abstract
The last decade has shown an increasing demand for 3D Geographic Information Systems (GIS) databases in many applications such as town planning, transportation, and utility management. The data acquisition is one of the core problems for building and maintaining such databases. The information needed is expensive to obtain by conventional techniques such as aerial photogrammetry and terrestrial surveying. These methods are, therefore, not well suited for rapid updating of GIS databases. In addition, conventional methods often supply only pointwise information and are inadequate for answering the increasingly complex questions concerning the interaction of different factors in urban centers and their associated time dependencies. Mobile Mapping Systems (MMS) that integrate navigation sensors and imaging sensors have been developed to the point that they can be used to create and update 3D databases very quickly and inexpensively. An example of such systems is the VISAT (Video-INS-SATellite) system developed by the University of Calgary, Canada. The VISAT is a precise mobile mapping van that can be operated at speeds of up to 60 km per hour and achieve a positioning accuracy of 0.3 m (RMS) for points within a 50 m radius of the van.

This paper will describe the development of the VISAT system and its softcopy photogrammetric workstation (VISAT Station). The VISAT Station implements the concept of storing georeferenced digital images as the basic unit for 3D coordinate determination. By combining an arbitrary number of such units, which may be from different time periods, the specific information required is obtained in any coordinate frame. The VISAT Station uses an SQL engine for building 3D databases that can be easily used directly or imported to any GIS software. It also implements a navigation window incorporating raster/vector base map or satellite images to display the van trajectory and the measured objects on user-defined layers to give a preview of the final product. The VISAT database are structured in such a way that it permits the export of all or part of the database from the navigation window or by using simple SQL scripts. Criteria such as the date of measurements, geographical area, or type of object (Fire hydrants, Traffic lights etc.) can be used to export a subset of the database. VISAT Station is also an Object Linking and Embedding (OLE) server. This allows any other GIS software to access the particular image that shows any object contained in the 3D database. The general structure of the 3D database will be discussed in more detail followed by a mathematical description of some of the automated techniques used in the VISAT Station such as back-projection and data-fusion with other georeferenced media.