ANALYTICAL AERIAL TRIANGULATION THROUGH EXTERIOR ORIENTATION

Abstract

Conventional methods of aerial triangulation are through relative-absolute orientation sequences.. The present dissertation deals with a different approach of aerial triangulation through exterior orientation geometry in which no stereomodels are created and the co-ordinates ' of pass points are directly recovered from exterior orientation geometry of photograms. Some successful investigations in this direction were made by Dr. H.L. Oswalt in his Ph.D thesis, in 1970, at University of Floor ke e and inspired from that some more investigations using more numbers of hypothetical photogi'ammetric strips/ blocks are undertaki4eti g to further investigate into the suitability of the following three methods for photo-grammetric control extension. i) Modified Earl Church Method ii) Oswalt s Iterative Method B iii) Smith' s Explicit Method Suitable computer programs were developed in Fortran IV for DEC-2050 system for planimetric aerial triangulation as well as for spatial aerial triangulation using all the above methods. Experiments on planimetric aerial triangulation were carried out in mode A (using 4 control points) and mode B (using 3 control points) for Modified Earl Church Method and Oswalt s Iterative Method B and in mode B only for Smith' s Method. Experi-ments on spatial aerial triangulation for all methods were iv conducted in mode A using 4 control points in supe rl ap region (except Smith' s Method) and modes B, C and D using 3 control points in different configurations. The results of planimetric aerial triangulation in mode A for Modified Earl Church Method and Oswalt s Iterative Method B are very good and nearly of similar nature whereas the corresponding errors are comparatively larger in mode B, though systematic, and proper adjustment of errors may produce fairly good results. Experiments on planimetric as well as spatial aerial triangulation using Smith' s Method. have produced quite large accumulation of errors in mode B and further investiga-tions are required including checking and computer program to draw any definite conclusion. Investigations on spatial triangulation by Oswalt s Iterative Method B have produced very good results in mode A as compared to the results of Modified Earl Church Method mode A. Experiments on spatial triangulation by Modified Church Method mode A produced large accumulation of errors whereas comparatively better results are obtained in mode B of the same rrethod which uses three control points, as compar-ed to 4 control points in mode A. Experiments were also carried out in modes C and D for spatial aerial triangulation using Oswalt s Iterative Method B and Modified Earl Church Method but satisfactory results were not obtained. From the present investigations it is found that Oswalt s Iterative Method B has produced better results amongst all the three methods used for aerial triangula-tion. Though equally good results have been obtained from Modified Church Method in all experiments except in case of spatial triangulation in mode A. It may, however, be concluded that photogrammetric control extension through exterior orientation approach is possible. It is recommended that further investigations should be carried out for more number of theoretical and actual photogrammetric strips/blocks using exterior orientation methods of aerial triangulation alongwith adjustment of errors. It is further recommended that aerial triangulation expei-iments be simultane(Jusly performed-on the same strips/blocks using conventional approach to enable direct comparison of the results of the two