Karsten Jacobsen 
  
  
may be located one beside the other or even with a vertical 
displacement of the flight lines (figure 2). The classical 
location of one flight axis beside the other has the advantage 
of the same photo scale, this makes the determination of tie 
points more easy. Only for a single flight strip or a 
combination of single flight strips, attitude data are required 
in addition to GPS-coordinates of the projection centers if no 
control points are available, because of the problem with the 
lateral tilt. But even for a real block structure, the combined 
use of GPS and IMU in the aircraft has some advantages. In a 
combined computation of the IMU- and GPS-data by a 
Kalman filtering, GPS cycle slips can be determined and so 
the problem of shifts and drifts of the GPS-data, different 
from flight strip to flight strip can be solved. In such a case, 
the crossing flight strips are not directly required, but they do 
Figure 3: relation GPS-antenna and IMU to the have the advantage of a better control of the block geometry 
camera — offset and misalignment and they are avoiding also problems of a not accurate lateral 
tilt of long flight strips. 
If not a very high accuracy is required, with the combined use 
of GPS and IMU the sensor orientation can be determined directly also without knowledge of image coordinates. As 
result of the Kalman filtering we will get roll, pitch and yaw of the IMU and the coordinates of the GPS antenna. The 
axis of the IMU will not be parallel to the photogrammetric camera — this boresight misalignment has to be determined 
by means of a reference bundle block adjustment. The stability of the boresight misalignment has to be checked - the 
photogrammetric cameras have not been constructed for the attachment of the IMU with the sufficient stability. The 
antenna offset from the camera projection center to the antenna and to the IMU has to be determined. It is not sufficient 
to use the orientation information of the IMU for the reduction of the GPS-position from the antenna to the projection 
center because usually the camera is rotated within the aircraft for the aircraft drift correction. Only if the antenna is 
located exactly above the camera, this can be avoided. Otherwise the rotation of the camera against the aircraft has to be 
recorded. 
  
    
  
GPS antenna 
    
Camera 
  
  
  
2 PROJECTS 
In cooperation with BSF (Berliner Spezialflug Luftbild und Vermessungen GmbH, Diepensee) and IGI Hilchenbach a 
larger block has been handled. The location of 2856 images taken in 4 flight days are shown in figure 4. Every day the 
misalignment and systematic GPS-position-errors have been determined before and after the flight over the main area 
by means of a small reference area located north of the block. In addition, for checking purposes, a sub-block with 252 
images and another with 460 images have been determined by combined block adjustment without IMU, so 
independent reference data are available. 
  
  
4 
m 
D 
ce eheduhe = pedesen 
3 Figure 4: configuration of the project 
P 7 area 
, + | The inertial measurement unit LCR88 
was mounted on top of a LMK 2000. 
An additional IMU, fixed to the aircraft, 
has been used for the reduction of the 
antenna position to the projection 
center. The: flying height. . of 
approximately 1090m above terrain 
corresponds with the focal length of 
305mm to a photo scale 1 : 3500. The 
direct orientation of a normal angle 
camera is more difficult than the 
+ | handling of a wide angle camera, 
approximately the double accuracy is 
required for the attitude data and the 
senes | program system BLLIH determination of the misalignment is 
  
  
  
  
  
  
  
AMA 
ER 
ie 
  
  
  
  
430 International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B3. Amsterdam 2000.