A REVIEW OF RADIAL STRIP TRIANGULATION METHODS WITH LIMITED INVESTIGATIONS ON A RECENTLY INTRODUCED ANALY TICAL PROCEDURE

Abstract

In photogrammetry, aerial triangulation is the method of multiplying ground control and this is achieved by strip triangulation or block triangulation methods. Both strip and block triangulation have procedures which generate control points either only in planimetry or both in plani-metry and altimetry. Radial strip triangulation is that form of aerial triangulation for strips in which control points are generated only in planimetry. Radial triangula-tion methods can give sufficient accuracy for plotting of topographic maps of the area having low topography. Control points obtained by radial triangulation can be used to obtain rectified photographs. And if the photography is good direct tracing methods can give good maps of such areas. That part of our country which has low topography can thus be quickly mapped. In the present work, different methods of radial strip triangulation are discussed. Section I is devoted to discussi of preparation of triangulation, choice of radial centres, errors of radial assumption, different methods, adjustment and propagation of errors. A recently introduced computational method of analytical radial triangulation by C.M.A.v.d.Hout is discussed in details. Limited experimental investigations made by the author on a strip of twelve photographs are described in • 1 Section II. Analytical radial triangulation method is used for triangulation. Computations are done by both v.d. Hout's recent method of using triangle chain as unit and old traditional method of using rhomboid chain as unit for computation. The standard error figures for coordinates of pass points obtained by both methods do not differ significantly. However, it is concluded the v.d. Hout's method is simple compared to old method as far as procedure of computation and programming is concerned. The computations can be done in few steps and programming is also not comparatively complicated. Thus much time and labour can be saved by use of Hout's method of analytical radial triangulation. Computer programs developed by author are given in Appendix - E.