Text 18

Выражения:

differ from		отличный от
in addition		кроме того
result in		выражаться в
in view of		учитывая
regardless of		независимо от
than ever before		чем когда-либо раньше
satisfy requirements		удовлетворять требованиям
launch site		пусковая площадка

Discrepancies Between Datums

In areas of overlapping geodetic triangulation networks, each computed on a different datum, the coordinates of the points given with respect to one datum will differ from those given with respect to the other. The differences occur because of the different ellipsoids used and the probability that the centers of each datum's ellipsoid are oriented differently with respect to the earth's center. In addition, deflection errors in azimuth cause a relative rotation between the systems. Finally, a difference in the scale of horizontal control may result in a stretch in the corresponding lines of the geodetic nets.

In view of the different orientation of ellipsoid centers, the relative rotation between the systems, and the scale differences; the computation of geodetic information from one datum to another unconnected datum is quite impossible. Regardless of the accuracy of the individual datums for computation within themselves, there is no accurate way to perform distance and azimuth computations between unconnected geodetic systems.

With the development of both intermediate and long range defensive weapon systems, geodetic problems have become more critical than ever before. To satisfy military requirements, it is necessary to provide detailed cartographic coverage of areas of strategic importance and to accomplish geodetic computations between these areas and launch sites which are often on unrelated datums. Both of these requirements necessitate unification of major geodetic datums by one or a combination of existing methods.

Text 19

Выражения:

of a limited scope		с ограниченным обзором
be restricted to …		ограничиваться ч-н
to fit each other		подгонять одно к другому

Datum Connection

There are three general methods by which horizontal datums can be connected. The first method is restricted to surveys of a limited scope and consists of systematic elimination of discrepancies between adjoining or overlapping triangulation networks (Figure 18). This is done by moving the origin, rotating, and stretching networks to fit each other. The method is usually used to connect local surveys for mapping purposes. This method of datum transformation or datum reduction can only be used where control exists for common points in different systems.

In addition to the classic method of datum transformation described above, there is the gravimetric method of Physical Geodesy (Chapter V) and the methods of Satellite Geodesy (Chapter VI). These methods are used to relate large geodetic systems to each other and/or to a world system (Chapter VIII). Both the gravimetric and satellite methods produce necessary "connecting" parameters from reduction of their particular observational data.