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Fusion of sensor data, knowledge sources and algorithms for extraction and classification of topographic objects
Baltsavias, Emmanuel P.

International Axchives of Photogrammetry and Remote Sensing, Vol. 32, Part 7-4-3 W6, Valladolid, Spain, 3-4 June, 1999
U. Stilla, K. Jurkiewicz
Research Institute of Optronics and Pattem Recognition (FGAN-FOM), Eisenstockstr. 12, D-76275 Ettlingen, Germany,
KEYWORDS: Airborne Laser Data, Digital Vector Maps, 3D-City Model, Roof Reconstruction.
In this paper, we describe a procedure for generating building models from large scale vector maps and laser altimeter data. In
contrast to other approaches, the map information is not used to form hypotheses about the roofs. Our approach permits the
recognition of additional structures as superstructures, which can not be derived from building outlines shown in the map. First, the
vector map is analyzed to group the outlines of buildings and to obtain a hierarchical description of buildings or building complexes.
The base area is used to mask the elevation data of single buildings and to derive a coarse 3D-description by prismatic models.
Afterwards, details of the roof are analyzed. Based on the histogram of heights, flat roofs and sloped roofs are discriminated. For
reconstructing flat roofs with superstructures, peaks are searched in the histogram and used to segment the height data. Compact
segments are examined for a regular shape and approximated by additional prismatic objects. For reconstructing sloped roofs, the
gradient field of the elevation data is calculated and a histogram of orientations is determined. Major orientations in the histogram are
detected and used to segment the elevation image. For each segment containing homogeneous orientations and slopes, a spatial plane
is fitted and 3D-contours are constructed. In order to obtain a polygonal description, adjacent planes are intersected and common
vertices are calculated.
Three-dimensional city models find more and more interest in
city and regional planning. They are used for visualization, e.g.
to demonstrate the influence of a planned building on its
surroundings. Although there is a great demand for such
models in mission planning and as basis for simulation, e.g. in
the fields of environmental engineering for microclimate
investigations (Adrian and Fiedler, 1991) or
telecommunications for transmitter placement (Kiimer et al.,
1993), current methods for their generation are expensive and
very time-consuming, involving extensive manual work.
In developed countries during the last years, many maps have
been stored digitally and are additionally available in vector
form. Large scale topographic maps or cadastral maps show
ground plans with no information on height of buildings or
shape of the roof. So far, information on height was derived
from ground surveys or from stereo pairs of aerial images.
Nowadays, elevation data are commercially available from
airborne laser scanners (e.g. Lohr, 1998). Knowing the precise
position and orientation of the airborne platform from
differential Ground Positioning System (dGPS) and Laser
Inertial Navigation System (LINS), 3D measurements of the
geographic position of surface points can be determined with
dm accuracy. The sampled surface points, distributed over a
strip of 250-500m width, allow the generation of a geocoded 2D
array with elevation data in each cell (elevation image). Single
flight strips are merged to a consistent digital elevation model
(DEM) of the whole survey area.
Fig. 1. 3D view of elevation data (Karlsruhe).
Fig. 2. 3D elevation data textured using an aerial image.
The reflected signal can be recorded and analysed in first pulse
and/or last pulse mode. While first pulse registration is the
optimum choice when surveying the top of objects (e.g.