Viking Orbiter stereophotogrammetry

Orbit characteristics of the two Viking Orbiter spacecraft made possible the acquisition of high-resolution imagery of the Martian surface, resulting in many excellent convergent stereopairs. Evaluation of these stereopairs presented a few unconventional problems because the routine relative orientation was not feasible, mainly due to a lack of good passpoints and to the technical peculiarities of TV vidicon imaging techniques. One of the ways to circumvent these problems is to use the orbital and navigational parameters of the spacecraft for an external 'forced' relative orientation. This approach requires a number of rotations and counter-rotations between various coordinate systems, which may make the involved mathematics look rather complicated, but its computational applications become very simple, fast, accurate, and inexpensive.