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THE EFFECT OF SYSTEM CALIBRATION ON DIRECT SENSOR ORIENTATION 
N. Yastikli 
Yildiz Technical University, Civil Engineering Faculty, TR-34349 Besiktas, Istanbul, Turkey 
ynaci@yildiz.edu.tr 
KEY WORDS: Photogrammetry, GPS, IMU, Direct, Sensor, Orientation 
ABSTRACT 
The determination of image orientation parameters of any sensor during data acquisition became possible by combined use of an 
inertial measurement system (IMU) and GPS. In this integrated system, GPS antenna, IMU and imaging sensor are located different 
position in airborne carrier. Because of this reason, the displacement vectors between sensors have to be determined. Similarly, axes 
of the IMU and imaging sensor are not same and a mis-orientation matrix exists between them. System calibration is including both 
calibration of individual sensor and calibration between sensors. The IMU calibration for drifts and biases and the calibration of 
imaging sensor for interior orientation parameter are components of sensor calibration. Calibration between sensors contains the 
determination of a constant displacement vector between sensors and a constant mis-orientation matrix between IMU body frame 
and imaging sensor frame. The boresight misalignment, the relation between the IMU and the imaging sensor is determined by 
bundle block adjustment using a calibration flight. The small change of correction of interior orientation and 3 shifts and 3 
misalignment angles between IMU and imaging sensor directly affect direct sensor orientation. 
In this study, the effects of the system calibration on direct sensor orientation is investigated based on data set of the test ‘Integrated 
Sensor Orientation? of the European Organization for Experimental Photogrammetric Research. For this, bundle block adjustments 
have been done with different approach using calibration flights. Using these bundle block adjustments, correction for interior 
orientation and 3 shifts and 3 misalignment angles between IMU and imaging sensor have been determined. The object coordinates 
of measured image points have been intersected based on GPS/IMU data improved by the boresight misalignment. For each 
approach, computed checkpoints coordinates have been compared with given reference coordinates. The effect of system calibration 
on direct sensor orientation has been analyzed comparing results of different georeferencing results using different system 
calibration parameters. 
1. INTRODUCTION 
The image orientation is a key element for any kind of imagery 
from terrestrial, airborne or satellite based sensors. 
Traditionally, this task is solved indirectly by using bundle 
block adjustment in photogrammetry. Today, GPS supported 
aerial triangulation is successfully used many photogrammetric 
map production projects. For new sensors such as LIDAR, SAR 
sensor and CCD line cameras, this indirect method can not be 
used because of the requirement of exterior orientation 
parameters for each scan line (Schwardz at all, 1993). The 
direct measurement of image orientations during image 
acquisition is appropriate solutions for these sensors using 
GPS/IMU system. By combined use of GPS and IMU (Inertial 
Measurement Unit), the direct measurement of exterior 
orientation parameters (Xo, Yo, Zo and o, q, x) of any sensor 
became possible. The GPS/IMU integrated system also can be 
used traditional field where bundle block adjustment is used. 
The georeferencing of images, recorded by different sensor can 
be defined as a transformation problem. For traditional 
photogrammetric cameras, this problem cover transformation 
form the image coordinates in camera coordinate frame to the 
mapping frame. To the georeferencing aerial images, the 
interior and exterior orientation parameters have to be 
determined. In this context, direct sensor orientation can be 
described as the determination of the sensor orientation 
parameters based on  GPS/IMU data respecting the 
(e.g. sensor calibration). Based on the direct georeferencing, 
c 
determination of the geometric information of the used sensor 
object coordinates corresponding to measured image points are 
determined. 
The direct sensor orientation is based on GPS and IMU data 
integrated with Kalman Filter. Three orthogonal mounted 
gyroscopes and three accelerometers are the components of an 
IMU. In some publication, the term inertial navigation system 
(INS) is used instead of IMU. INS contains an IMU as a 
measurement device as well as positioning and guidance 
functions (Colomina, 1999). 
Inertial navigation systems were at first developed for military 
navigation applications in 1968. During the 1970s, the 
surveying community realised that INS or GPS/INS integrated 
system can be used as a survey instrument. In the late 1980s 
and early 1990s experimental studies have been done by the 
Ohio State University and the University of Calgary (for 
details, see Scherzinger B. M., 2001). In resent years, a series of 
tests, pilot projects and several publications confirmed the 
accuracy performance of direct georeferencing and integrated 
sensor orientations (Schwarz at al, 1993; Schwarz, 1995; 
Skaloud et al., 1996; Jacobsen, 1999; Colomina, 1999; Cramer, 
1999; Skaloud 1999; Heipke et al., 2001; Mostafa and Schwarz, 
2001). 
In the following, the effect of system calibration on direct 
sensor orientation and not correct data handling are investigated 
based on the data set of the test ‘Integrated Sensor Orientation’ 
of the European Organization for Experimental 
Photogrammetric Research (OEEPE).