of 
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Ismael Colomina 
T.O.P. CONCEPTS FOR SENSOR ORIENTATION 
Ismael Colomina 
Institute of Geomatics 
Generalitat de Catalunya & Universitat Politécnica de Catalunya 
Barcelona, Spain 
ismael.colomina Q IdeG.es 
KEY WORDS: aerial triangulation, automatic aerial triangulation, Galileo, GPS, IGS, INS, INS/DGPS, sensor calibra- 
tion, sensor orientation. 
ABSTRACT 
Airborne sensor orientation, particularly for photogrammetric cameras, is of interest because orientation is a key step, 
between acquisition and iterpretation, which determines the quality and even the interpretability of images. In this paper, 
a global approach to sensor orientation is presented with emphasis on aerial photogrammetric cameras. The situations 
where a pure INS/DGPS solution suffices and where a combination INS/DGPS/AT is required are discussed as well as their 
global and local aspects. The discussion is linked to the current progress in GPS technology and the future development 
of the European Galileo system. 
1 INTRODUCTION 
In the late eighties, the first successful AT/DGPS (Aerial Triangulation and Differential GPS) experiments were com- 
pleted. Today, a decade later, direct sensor orientation by INS/DGPS has become the dominant orientation technology for 
all airborne sensors with the exception of metric aerial cameras. In this particular area, the success of automatic digital 
terrain model generation for orthophoto production has encouraged the development of AAT (Automatic AT) by digital 
image matching. As a result, in addition to standard AT/DGPS, two different technologies, INS/DGPS and AAT/DGPS, 
are available. In parallel, satellite geodetic positioning has made enormous progress. If we look at all these developments 
and compare them with current practices, the idea of their optimal combination for photogrammetric camera orienta- 
tion comes naturally. The name Total Orientation Procedures (Colomina, 1999) intends to reflect this approach which is 
qualitatively discussed in the rest of the paper. 
2 ON TWO-STEP ORIENTATION 
Sensor orientation is only a step, a “technicality” in the process of image exploitation whose ultimate goal is image 
interpretation. 
The mapping and cartographic pattern acquisition-normalization-interpretation is not a particular one in the area of geo- 
sciences and Earth observation. In all cases, between raw data acquisition and data exploitation or interpretation, there is 
an intermediate step which has to correct raw data from instrumental errors and external influences before data is amenable 
for specific domain interpretation. In physical geodesy interpretation is geoid determination, in mineral exploration inter- 
pretation is mineral location. 
Normalization serves therefore interpretation. Normalization is technology-dependent; much more than interpretation is. 
Interpretation sets the requirements for normalization or, in our context, sensor orientation. The requirements are of many 
different kinds, from operational to geometrical, from technical specifications to time and cost constraints. 
Within the technical requirements both the precision, accuracy and reliability figures as well as the more qualitative aspects 
like consistency with local reference frames or parallax-free stereo models are found. 
Traditionally, the photogrammetric orientation task is usually performed in two separate steps: in the first step (aerial 
triangulation or INS/DGPS trajectory determination) the long wavelength components [or global solution] of position 
and attitude are solved for; in the second step (stereo model set-up) the short wavelength components [or relative local 
solution] are resolved. The first step delivers orientation at accuracy levels which meet project geometric specifications. 
It guarantees the overall block consistency. In an orthophoto project, for example, this is enough since there is no stereo- 
scopic interpretation task at the end of the production line. In a standard topographic mapping project, orientation has 
to serve another task, namely, stereoscopic image visualization and interpretation. In this case, the short wavelength 
  
International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B3. Amsterdam 2000. 191