|o ct e oJ M MM 
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ISPRS Commission III, Vol.34, Part 3A »Photogrammetric Computer Vision“, Graz, 2002 
5.1 Results 
The indirect georeferencing algorithm described in Equation 6 
was tested in order to estimated the parameters modelling the 
sensor external orientation and the ground coordinates of the 
TPs. From the available 40 object points, a group of them was 
used as GCPs and the remaining as TPs. The TPs ground 
coordinates estimated by the triangulation were compared to 
their correct values and used for the tests’ control. Various 
combinations of GCPs and TPs were chosen in order to 
evaluate the influence of the ground information. Table 1 
provides a summary of the resulting absolute accuracy in the 
different test configurations. 6, 10 and 20 GCPs were tested, 
using 5 and 10 segments for the external orientation modelling. 
An absolute accuracy in the range 4-13 cm for X, 3-12 cm for Y 
and 8-19 cm for Z were achieved, corresponding to 0.6-2.1 
pixels, 0.2-2 pixels and 1.3-3 pixels. Anyway the fact that the 
image coordinates were estimated at 0.5 pixels accuracy could 
have affected the results. The comparison between the results 
from the different tests confirms that the triangulation accuracy 
is influenced by the number and distribution of ground 
information and improves with the number of GCPs. As far as 
the modelling functions are concerned, the division of the 
trajectory in a larger number of segments does not imply any 
substantial improvements. 
  
GCPs+ TPs 
20+20 | 10+30 | 6+34 
RMS, 150.070 170.082 | 0.131 
5 segments RMS, | 0.028 | 0.088 | 0.090 
RMS; | 0.086 | 0.172 | 0.146 
RMSy | 0.041 | 0.050 | 0.057 
10 segments | RMSy | 0.059 | 0.099 | 0.124 
RMS; | 0.112. | 0.138 | 0.192 
  
  
  
  
  
  
  
  
  
  
  
  
  
  
Table 1. RMS values (in meters) of the estimated 
TPs coordinates. 
6. CONCLUSIONS 
A general sensor model for multi-line CCD array sensors with 
along stereo viewing has been presented. The model combines 
the classic photogrammetric collinearity equations with the 
sensor external orientation modelling, resulting in an integrated 
triangulation. The functions used to describe the external 
orientation are based on piecewise polynomials. The model can 
be applied on sensors carried on both airplane and satellites, 
with optical systems consisting of one or more lenses. The 
algorithm can also include and correct any external orientation 
observations provided by GPS and INS instruments carried on 
board. 
The proposed model has been tested on a simulated sensor (1 
lens, 3 CCD arrays) carried on airplane, with different GCPs 
and TPs distributions. The results have been presented. An 
accuracy in the range of 0.6-2.1 pixels in X, 0.2-2 pixels in Y 
and 1.3-3 pixels in Z was achieved using 6, 10 and 20 GCPs 
and dividing the trajectory in 5 and 10 segments. 
In the next future, the model will be applied to a real dataset 
from the Japanese TLS (Three-Line Sensor) by Starlabo, 
Tokyo. 
7. ACKNOWLEDGMENTS 
This work is part of Cloudmap2 project, funded by the 
European Commission under the Fifth Framework program for 
Energy, Environment and Sustainable Development. 
I would like to thank Mr. Zhang Li, from my department, for 
his helpful suggestions. 
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