1 fusion 
> points 
ters are 
of the 
optimal 
cessing 
surface 
merged 
s. This 
such as 
irface is 
' data to 
g Ocean 
vely, are 
' surface 
e initial 
immetric 
fficiency 
medium 
th abrupt 
formance 
like lack 
ntinuities 
weas and 
altsavias, 
pixels in 
ldings or 
ntinuities 
97). The 
requency 
by many 
an et al., 
id. Kilian, 
ave been 
the data 
of surface 
ala et al., 
high-rise 
points is 
Kerry McIntosh 
  
Figure 1. Plan view showing laser data. 
Investigations and observations comparing DSMs produced from laser data and those derived from digital 
photogrammetric methods have been made in several research studies. In areas of the imagery lacking texture or 
contrast, the image matching might not provide accurate results whereas the accuracy of the laser is not affected 
(Baltsavias, 1999; Kraus and Pfeifer, 1998), however photogrammetric data have a higher planimetric accuracy than 
laser data (Baltsavias, 1999). 
The complementary nature of the two data sources has been widely recognized and the approach of combining them has 
been suggested by researchers for several years (Fritsch and Kilian, 1994; Haala, 1994). This suggestion has been 
reiterated recently (Ackermann, 1999; Axelsson, 1999; Baltsavias, 1999; Csathó et al., 1999; Fritsch, 1999: Haala, 
1999; Haala and Anders, 1997; Toth and Grejner-Brzezinska, 1999; Vosselman 1999). The approach of using imagery 
to provide edge information has been highlighted by several researchers (Ackermann, 1999; Axelsson, 1998; Csathó ef 
al., 1999; Haala and Anders, 1997), and is the main concept of the approach undertaken in this research (McIntosh, ef 
aj... 1909), 
3 PROPOSED DATA INTEGRATION APPROACH 
The research presented in this paper utilizes information from laser scanner data and photogrammetric data to produce 
an accurate model of the visible surface. By merging the edge information and the laser data for surface generation, a 
DSM is produced that more closely represents the actual scene. 
3.1 Surface Registration 
The surface registration is undertaken to determine the transformation parameters between the laser surface and the 
photogrammetrically derived surface. Theoretically, the two data sets should be on the same coordinate system, 
however the systematic errors inherent in the laser data may introduce a misalignment between the two surfaces, which 
must be eliminated before data fusion may be performed accurately (Kraus and Pfeifer, 1998). 
The transformation parameters are used to convert the laser data to the coordinate system of the photogrammetric data. 
The determined transformation parameters must be as accurate as possible to ensure no unnecessary degradation occurs 
in the accuracy of the surface generated from merging the data sets. 
The algorithm was developed specifically for matching visible surface models of urban areas produced using different 
acquisition methods, and in particular, surfaces from airborne laser scanner data and surfaces automatically generated 
using photogrammetric data. The registration algorithm solves for three translation parameters, three rotation 
parameters and one scale factor. The surface points are not interpolated to a regular grid and there are no identifiable 
conjugate points in the surfaces. For more detailed information on the algorithm and the results of testing, the reader is 
referred to Schenk er a/. (2000). Another approach for matching such surfaces is given by Habib and Schenk (1999). 
3.2 Data Fusion 
The data fusion component utilizes edges extracted from stereo imagery to obtain accurate locations of surface 
discontinuities. The edges are defined in three dimensions and are used as breaklines when merged with the 
transformed laser data. A new surface is generated using the merged data, which is expected to have a higher accuracy 
than the surface derived from either of the separate data sets. The conceptual approach formulated in this research 
proposes that the edges representing surface discontinuities are automatically derived as 3D line segments from the 
stereo imagery using edge extraction and feature matching techniques. Research has been undertaken into the 
  
International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B3. Amsterdam 2000. 
un 
e 
Un