CONJUGATE POINTS IN THE ORIENTATION OF 
ACROSS AND ALONG TRACK STEREOMODELS 
FRANCELINA A. NETO 
64), pp. Professora Auxiliar 
Departamento de Matemática Aplicada 
Universidade do Porto 
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Geodesy Forusal 
Commission III, Working group 1 
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men), Sinn ; 
KEY WORDS: Orientation; Camera Model; Conjugate Points; SPOT; OPS 
on of 
mission Ill ABSTRACT: 
982. In 
Conjugate points have long been used in the orientation of aerial and spaceborne imagery. In this study, a physical and 
polynomial model were used for testing the use of conjugate points in linear array imagery from higher altitude 
platforms. SPOT and OPS data were used for the tests, with the ultimate objective of reduction of the ground control 
needed for their orientation. The orientation models are summarised and the use of conjugate points is assessed. A 
summary of the results obtained is presented for different types of control configurations adopted. The several problems 
relation : found using conjugate points in the orientation of linear array imagery are discussed. The main draw backs found were 
frican that the algorithms become very time expensive and occasionaml problems of convergence arise. The use of weight 
id matrices and the information from the co-variance matrix does not help solve the problem. The results obtained show 
no advantage in adopting such method when enough control exists. However, this technique may be used to ensure a 
x: model orientation when the ground control is not enough on its own. The information extracted from conjugate points 
SION seems to be more helpful for the physical than for the polynomial orientation algorithm. The relative orientation of the 
ation, model shows little improvement for the former, while no improvement is registered for the latter. 
hing of 
op “From : : : 
227-234 1. CONJUGATE POINTS AND stereopair, for which the ground coordinates are 
ALGORITHM DEVELOPMENT unknown. Once introduced to the orientation model, 
squares conjugate points help improving the relative orientation 
Object Algorithms developed for the orientation of airbone and of the model. 
te spaceborne imagery usually make use of control points 
with known ground coordinates. However, the cost of a Linear array imagery is becoming increasingly important 
map product is directly dependent upon the cost of the for map production and revision. Although this type of 
ons and imagery orientation procedure, hence upon the number of imagery is more common from higher altitude platforms, 
control points used. Reducing the ground control to a and has lower resolution, robust orientation algorithms 
minimum is therefore a major concern during algorithm have been widely tested, with successful results. They 
| development. have been described in various bibliographies, and the 
2 results compared [Neto and Dowman, 1991]. In the case 
Most researchers direct their effort into the use of on- of SPOT, one main conclusion from these tests was that 
ng the board registered data. Such data vary with sensor and a minimum number of 6 ground control points would be 
9 platform, usually consisting of the position and velocity advisable for a best orientation without extra data. 
ing'and of the platform for regular intervals of time. These are Similar results were obtained for other data using 
usually very sparse in time and have to be interpolated simulation studies [Neto, 1993]. 
M : for the time of image acquisition. Other data usually also 
ethod : ; : quit : : : 
oed measured on-board are the platform attitude variations IGN has considered in the past the use of conjugate 
with time. The use of these data is proving to be very points for the orientation of SPOT imagery [Rodriguez et 
effient when introduced to the orientation algorithms. It al., 1988]. With the move toward along track linear array 
Surface improves the initial solution for the orientation satellite sensors, it becomes necessary to consider such 
parameters, especially those modelling the attitude of the data in any study of this type. For this reason, the author 
7-84 platform. studied the effect of using conjugate points in the 
Other techniques for the reduction of ground control 
have been explored with success in photography, such as 
the use of conjugate points. Conjugate points are 
common points identified on the photographs of a 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B3. Vienna 1996 
orientation of SPOT and OPS data, and analysed the 
effect on the reduction of the necessary ground control. 
This study was carried out using a physical and 
polynomial model of the orbit of the platforms. The 
physical model is summarised in this paper.