Aerophotogrammetry applied to the survey of large areas at mean scale

Abstract

Summary 1) Technical maps of scales varying from 1/100 to 1/10,000 may differ considerably one from another in their typical features. Consequently, the economy in the use of photogrammetric techniques in place of classical ground methods can only be established for each particular case. The references given here are to cadastral maps of large areas, and in this case it is proposed to show that photogrammetric methods are preferable from an economic point of view. 1) The original article has been published in Italian in Photogrammetria, 1949–1950, no. 4. If we compare the normal processes of this type of work executed by ground survey methods with the corresponding photogrammetric methods itis obvious that some of the processes are common to both methods, and that there are equivalent phases, such as, for example, “ground survey and small details plus land sketches plus geometric construction of the map” which are analogous to “flying plus plotting”. In order to illustrate the economies of the problem, the cost of the ground survey must be compared with the plotting performance which the air survey plotting instrument must produce. Eventually, it will be shown that the performance of the plotting instrument may or may not reach the desired efficiency. In 1934, the Italian Cadastre entrusted the photogrammetric production of the first cadastral maps to private enterprise, with the proviso that the cost should not exceed the estimated cost of the classical ground methods. The commercial undertakings accepted this condition, thus substantiating in some degree that the cost of the photogrammetric mapping of this type can be economically undertaken. Recently, in both Italy and Portugal there has been further competition in private enterprise for surveys on a scale of 1/1000, 1/2000 and 1/5000 in which the companies could make use of both ground and air survey methods. The result of the contracts accepted once again of both the higher economy of the photogrammetric method. Average costs for such surveys over large areas under the specification comparable to those of the Italian Cadastro are: