0 years, 
ation by 
ces their 
ground 
ith high 
ermany) 
| digital 
:chnical 
data as 
ente der 
lemente 
igen für 
e einem 
ors mit 
ion mit 
.ameras 
ssigkeit 
rungen 
uch als 
den. 
"n. 
International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B1. Istanbul 2004 
  
1. INTRODUCTION 
In the field of photogrammetry and remote sensing airborne 
sensors are more and more applicable. Hansa Luftbild 
German Air Surveys operates about 2000 hours per year of 
survey flights. The users are more and more requiring very 
fast, inexpensive and actual information. 
The most common airborne sensors are still the optical 
systems (passive) like film cameras or in a growing number 
digital cameras. Additionally active sensors like the airborne 
laser systems (LiDAR = Light Detection And Ranging) or 
InSAR (Interferometric Synthetic Aperture Radar) are more 
and more important. 
Users of all these sensors facing the same problem: it is 
necessary to know their 3-dimensional orientation during the 
time of detection of the information. This is known in 
photogrammetry as the determination of the exterior 
orientation parameters and is a standard procedure called 
aerial triangulation in the photogrammetric workflow. 
In order to avoid ground control as much as possible, 
differential GPS were introduced to measurle some of the 
elements of the sensor orientation in a direct way. Only in the 
last few years the direct measurement of all parameters of the 
exterior orientation (so called direct geo-referencing) by a 
combination of GPS and INertial System (INS) or Inertial 
Measurement Unit (IMU) was successful and could be 
offered at a reasonable price to the users. 
In the following some of the projects and findings for an 
GPS/INS system in practical use should be introduced. The 
experiences out of the projects from the point of view of a 
service company will be described. 
2. DIRECT GEO-REFERENCING 
The method of direct geo-referencing allows to transfer 
sensor or object data immediately into a local or global co- 
ordinate system, which makes their further processing 
possible (see figure 1). Such a system exists of receivers of 
the global positioning system (GPS) on board and on the 
ground (reference stations) and an inertial system combined 
with a sensor, which determines angles and accelerations of 
the sensor with high precision. 
Offsets between sensor and inertial system are determined by 
a calibration done by the user (boresight alignment). During 
post-processing, the GPS position is computed and the 
calibration results are taken into account. Finally the 
transformation from the global co-ordinate system (usually 
UTM /WGS84) to the requested local system has to be done. 
  
Fig. 1. Principle of direct geo referencing, Positioning 
(X,Y,Z) and rotations (®, ©, K) will be captured during the 
survey flight 
  
Fig. 2. GPS/INS system AEROcontrol™ by IGI, Kreuztal, 
Germany 
The components of the complete system AEROcontrol™ 
are (see figure.2): 
— Inertial system (INS) 
— 12 channel L1/L2 GPS receiver 
—  AEROcontrolTM computer 
— Flight management system CCNS 4 
— GPS reference station 
For post processing, the specific software AEROoffice!M by 
IGI is of course also needed. 
Hansa Luftbild German Air Surveys operates successfully 
since the year 2000 two GPS/INS systems AEROcontrol™ 
by IGI, Kreuztal, Germany. The IMU unit is on demand 
attached to the camera, taken from the company own pool of 
five Zeiss RMK TOP and several Zeiss RMK A with 
different focal length.