Eberhard Steinle 
  
EFFECTS OF DIFFERENT LASER SCANNING MODES ON THE RESULTS OF BUILDING 
RECOGNITION AND RECONSTRUCTION 
Eberhard STEINLE, Thomas VÖGTLE 
University of Karlsruhe, Germany 
Institute of Photogrammetry and Remote Sensing 
steinle@ipf.uni-karlsruhe.de 
voegtle@ipf.uni-karlsruhe.de 
KEY WORDS: Laser Scanner, Building Reconstruction, Urban Objects 
ABSTRACT 
Airborne laser scanner systems are of increasing importance for measurement of digital elevation models (DEM) and 
hence, for acquisition of 3D objects like buildings in urban areas. There are several approaches to the modelling of 
buildings by means of laser scanning data, but hardly any studies about comparison of the two possible scanning modes, 
first pulse and last pulse mode, concerning building reconstruction. In this paper, the effects of first pulse and last pulse 
measurement on the acquired DEMs are explained, some specific phenomena are described and suitability, i.e. the 
advantages and disadvantages of each scanning mode, for building reconstruction is discussed. Two examples illustrate 
the principle differences of the resulting building models, derived from first pulse and last pulse mode respectively. 
Finally, first experiences on deviations of these models from the correct building shapes (represented by manually 
measured CAD models) and on the achieved accuracy will be presented. 
1 INTRODUCTION 
Airborne laser scanning technique is of increasing importance for the acquisition of 3D objects, especially for building 
recognition and reconstruction in urban environment. There are several approaches for modelling of buildings by means 
of laser scanner data. Some of these use additional information sources like digital maps, spectral images or other GIS 
data, e.g. (Brunn & Weidner, 1998), (Haala et al, 1998), (Maas & Vosselmann, 1999) and (Vogtle & Steinle, 2000). 
Laser scanning systems can be distinguished with regard to the measurement principle. Most of the available systems 
use pulsed laser scanning, only a few are based on continuous-wave scanning. When using pulsed laser scanning, it is 
possible to measure the runtime of the laser signal in two different modes, first pulse and last pulse mode. For a better 
understanding of the effects on the captured data these principles are described in more detail in section 2. Generally, it 
is not possible to acquire laser scanning data in both modes simultaneously due to technical restrictions of the systems. 
Therefore, one of them has to be chosen before data acquisition, depending on the requirements of the specific 
application. Even if there are several attempts in using laser elevation data for building reconstruction, there are hardly 
any studies that discuss which of these two operating modes is more suitable in this context. 
Therefore, in this paper the effects of the different laser modes on the elevation data (DEM) and the results of building 
modelling are explained and special phenomena concerning data processing are described. Finally some examples from 
our test areas are given and the achieved accuracies as well as the advantages of each operating mode discussed. 
  
858 International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B3. Amsterdam 2000. 
  
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