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EXTRACTION OF FEATURES FROM OBJECTS IN URBAN AREAS USING SPACE- 
TIME ANALYSIS OF RECORDED LASER PULSES 
B. Jutzi *, U. Stilla ^ 
“ FGAN-FOM Research Institute for Optronics and Pattern Recognition, 76275 Ettlingen, Germany - 
jutzi@fom.fgan.de 
? Photogrammetry and Remote Sensing, Technische Universitaet Muenchen, 80290 Muenchen, Germany - 
stilla@bv.tum.de 
Commission II, WG IU2 
KEY WORDS: Urban, Analysis, Simulation, Laser scanning, LIDAR, Measurement, Feature. 
ABSTRACT: 
In this paper we describe a simulation system and investigations for analysis of recorded laser pulses. A simulation setup that 
considers simulated signals of synthetic objects was developed for exploring the capabilities of recognizing urban objects using a 
laser system. The temporal waveform of each laser pulse is analyzed for gaining the pulse properties: range, pulse power and 
number of peaks. Considering the received pulse power of the associated spatial neighborhood for the region boundary delivers the 
estimation of the edge position and edge orientation with sub pixel accuracy. 
c 
1. INTRODUCTION 
The automatic generation of 3-d models for a description of 
man-made objects, like buildings, is of great interest in 
photogrammetric research. In photogrammetry a spatial surface 
is classically measured by triangulation of corresponding image 
points from two or more pictures of the surface. The points are 
manually chosen or automatically detected by analyzing image 
structures. Besides this indirect measurement using object 
characteristics, which depends on natural illumination, active 
laser scanner systems allow a direct and illumination- 
independent measurement of the range. Laser scanners capture 
the range of 3-d objects in a fast, contactless and accurate way. 
Overviews for laser scanning systems are given in (Huising & 
Pereira, 1998; Wehr & Lohr, 1999; Baltsavias, 1999). 
Current pulsed laser scanner systems for topographic mapping 
are based on time-of-flight ranging techniques to determine the 
range of the illuminated object. The time-of-flight is measured 
by the elapsed time between the emitted and backscattered laser 
pulses. The signal analysis to determine the elapsed time 
typically operates with analogous threshold detection (c.g. peak 
detection, leading edge detection, constant fraction detection). 
Some systems capture multiple reflections, caused by objects 
Which are smaller than the footprint located in different ranges. 
Such systems usually capture the first and the last backscattered 
laser pulse (Baltsavias, 1999). Currently first pulse as well as 
last pulse exploitation is used for different applications like 
urban planning or forestry surveying. While first pulse 
registration is the optimum choice to measure the hull of 
partially penetrable objects (e.g. canopy of trees), last pulse 
registration should be chosen to measure non-penetrable 
surfaces (e.g. ground surface). Figure la shows a section of an 
image taken in first pulse mode. The foliage of the trees is 
visible. Figure 1b was taken in last pulse mode. The branches 
and folia 
e are not visible and the building areas are smaller 
than in Fi 
igure la. Due to multiple pulse reflection at the 
€ 
o 
© 
F 
1 > . . . - 
noundary of the buildings and the processing by first or last 
107 
pulse mode, building areas dilate or erode. For visualizing the 
various sizes of the building footprints in first and last pulse 
images a difference image is calculated (Figure Ic). The 
ambiguous pixels of the building are visible by a bright area 
along the buildings contours. A zoomed section of a building 
corner is depicted in Figure 1d. Building edges are expected 
within these bright areas. 
  
E 5 : N 
Fieure l. Sections of an urban scene (Test area Karlsruhe, 
Germany). 
a) elevation images captured by first pulse mode, 
b) elevation images captured by last pulse mode, 
c) difference image of first and last pulse mode, 
d) subsection of the difference image (building 
boundary ). ;