The overall scale and orientation of the South African trigonometrical readjustment will depend both on the traditional distances and azimuths and on TRANSIT Doppler observations. The traditional observations are used to compute the relative positions of points within the control network. TRANSIT Doppler observations, as well as giving relative positions, can be used to determine absolute co-ordinates (in a global reference system) with an accuracy of about one metre. One purpose of the present study is to present a way of combining the various Doppler observations to the TRANSIT satellites and to derive a single set of geocentric co-ordinates for the stations at which Doppler observations were recorded. Little work has been published concerning the combination of such Doppler observations. Having arrived at a set of geocentric co-ordinates, in order to use them in the horizontal adjustment, they must be transformed to latitude, longitude and height with respect to a defined ellipsoid. The second purpose of the present study is to examine various criteria for choosing such a datum and thereby make a suitable datum selection. There are various ways of processing observations to the TRANSIT satellites; these techniques along with the rest of the Doppler system are described in chapter 3. Chapter 4, which contains the bulk of the work in the present study, addresses the problem of the unification of Doppler subnets into a single geocentric network. Chapter 1 contains an introduction and gives a brief overview of the various reference systems used in Geodesy while Chapter 2, which is largely historical, describes the existing geodetic network in South Africa, particularly the Cape Datum on which this network is computed. In chapter 5, using the co-ordinates for the Doppler stations derived in chapter 4, various criteria are considered for the selection of a datum on which to carry out the readjustment and recommendations are made for a replacement South African geodetic datum.

Bibliography: pages 134-140.