Springer, 
ocessing 
Analysis 
October 
, Ottawa, 
)93 IERS 
ureau of 
the IGS 
14, 1993, 
Global 
oy for 
1992, in 
esy to 
Smith, 
ics Series 
. Union, 
AIRCRAFT POSITION AND ATTITUDE DETERMINATION BY GPS AND INS 
Klaus-Peter Schwarz, The University of Calgary, Canada 
KEY WORDS: 
Direct Georeferencing, exterior orientation, GPS/INS integration, airborne position and attitude accuracies. 
ABSTRACT 
The parameters of exterior orientation for airborne imaging sensors, i.e. position and attitude of the sensor at each 
exposure, can be obtained by integrating GPS and INS. By matching the accuracy of the external orientation 
parameters to the accuracy required on the ground, photo control is not needed any more to estimate parameters of 
exterior orientation. This greatly reduces the requirements for ground control which can now be configured to optimize 
camera calibration and transformation to a local coordinate system, where needed. The full potential of this approach 
for non-conventional airborne sensors, such as imaging scanners and digital frame cameras, is only now being 
explored, although some of the underlying ideas have been partially applied for several years in GPS-aided block 
triangulation. The paper briefly reviews the principle of airborne georeferencing and its implementation by using an 
inertial navigation system (INS) integrated with differential GPS. The position and attitude performance of INS and 
GPS are discussed and INS/GPS integration strategies are analysed. Results show that the present accuracy of 
INS/GPS integration is sufficient for many of the current and emerging mapping and resource applications. 
1. INTRODUCTION 
During the last three decades, airborne photogrammetry, 
when applied to mapping, has been performed in a single 
mode of operation: aerotriangulation with block 
adjustment of either bundles or stereo models. This 
mode was well justified by operational constraints. 
Because ground control was usually scarce, the 
geometrical strength of the bundle had to be used to the 
fullest. By creating homogeneity within the 
photogrammetric block, smooth residual errors could be 
expected which could be well appoximated by simple 
interpolation procedures between a few date points. 
With the advent of reliable methods of kinematic GPS 
positioning, the interpolation component of the process 
was considerably improved. By being able to position the 
projective center of each exposure with high absolute 
accuracy, the translational components of the block 
configuration were strengthened, and position biases, 
scale factors, and drifts in latitude and longitude could be 
estimated with high accuracy, independent of existing 
ground control. In addition, camera calibration became 
' much easier provided a few ground control points were 
available either in the area or close to it. The orientation 
component was indirectly strengthened because 
coordinate constraints between exposure stations also 
constrained the relative orientation between adjacent 
bundles. The fact that this introduced a high correlation 
between translation and orientation components seemed 
not to be critical in practice because the geometrical 
strength of the individual bundle was comparable in 
accuracy to the derived orientation changes. Thus, GPS- 
aided aerotriangulation in block adjustment mode has 
emerged as the optimal procedure for those applications 
requiring high-precision optical cameras and area 
coverage, see for instance Ackermann (1994), Hothem et 
al. (1994), Lukas (1994), for details. 
  
This paper is an updated and abbreviated version of Schwarz 
(1995) published in 'Fritsch/Hobbie (eds.) Photogrammetric Week 
'95, Wichmann Verlag’ 
67 
The paper, therefore, addresses applications where these 
conditions are not satisfied, i.e. either situations where 
sensors other than high-precision optical cameras 
areflown or strip or model coverage rather than block 
coverage is required. In these applications, external 
orientation becomes as important a parameter as 
external position has become in GPS-aided 
photogrammetry. The reason for this is that either the 
sensors used do not have the same geometrical strength 
as high-precision aerial cameras or that the photo 
coverage is such that the geometrical strength of the 
bundle for relative orientation is not sufficient. In the first 
case, digital frame cameras and line scanners come to 
mind. In the second case, highway and powerline design, 
coastal mapping, and pipeline maintenance could be 
mentioned. Since each individual image is now 
georeferenced, i.e. the parameters of interior and exterior 
orientation in each image are known, ground control is 
not necessary to derive these parameters. This provides 
considerable flexibility for post-mission modelling which 
now can be done with georeferenced images as the basic 
unit. The accuracy of the method obviously depends on 
the accuracy with which the georeferencing parameters 
can be determined. This question will be analyzed in the 
following. 
2. GEOREFERENCING OF AIRBORNE SENSORS 
Georeferencing of airborne sensors is treated in some 
detail in Schwarz et al. (1993), A brief review of the major 
concepts will be given here to provide a framework for 
the following discussion. Georeferencing describes a 
series of transformations necessary to obtain coordinates 
in a chosen mapping system (m) from the output of a 
remote sensing device in the body frame (b) of the 
aircraft. The important parameters for this transformation 
are depicted in Fig. 1. 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B6. Vienna 1996