3 
AEROTRIANGULATION ON THE AP/C *’ 
1. - There are already several papers dealing with the Analytical Plotter built by the O. M. I. 
of Rome and by the Bendix Corporation of Detroit, and some of them are very recent. In the 
bibliography we have listed some of the most significant, since this extensive literature dispenses 
us with even a short description of the instrument, of the construction principles and of the ope 
rative procedure that it allows. 
When in March 1964, for kind concession of O. M. I., an Analytical Plotter was installed at 
the « Centro di Addestramento e Studi Fotogrammetrici» (C. A. S. F.) of Milan, the aim of the 
researches that we have planned after a short period of training of the operators, was mainly to 
experiment the aerotriangulation on this new instrument. In fact, even if several authors, the 
inventor himself and the builders had already shortly described the operations necessary for the 
execution of aerotriangulation, no systematic experimental work had yet been carried out. 
The C. A. S. F. intended that the present research would test the routine of aerial triangulation, 
according to the most simple and schematic procedure, and evaluate the measuring accuracy and 
the computation performances. At the same time, a wider future program of investigation has 
been planned even if, so far, it has only been briefly outlined. This program should include a 
more accurate study of the facilities offered by the computer and then a search for solutions more 
general and appropriate to the instrument at our disposal, solutions that should differ from the 
schema of the analogical plotter which is still applied. 
Of the future investigations the present research is only a necessary, though modest premise. 
2. - The tests made in order to determine the degree of mechanical accuracy of the instrument 
are of the two following types: 
a) plotting of single models obtained by means of precision grids; 
b) triangulation of fictitious strips whose single photograms are made by precision grids. 
a) The model has been formed with the usual procedure after having placed on the plate 
holders two grids whose meshes have 1 cm side. For the interior orientation we have imposed 
a focal length of 100.35 mm > a size 140 x 140 mm 2 , an overlapping of about 60 % and a ratio 
Z/f = 1.2. The model has been relatively oriented on the 6 standard points, by a numerical pro 
cedure. For the absolute orientation we have used the same six points, giving to all of them the 
same ground height. Moreover, the model has been planimetrically oriented so that the first 
three model points had the same Y coordinate. 
In each model we have then plotted 32 points corresponding to the crossings of a grid with 
2 cm meshes and 140 x 60 mm 2 size (see figures 1 and 2). The X, Y, Z coordinates and the residual 
parallax have been measured twice for each point represented by a crossing. We have then 
computed the means for each coordinate and for b y on the 32 plotted points and then the single 
discrepancies and their mean square values. No correction has been given to the points coordinates 
in order to improve the dimensions and orientation of the model obtained through the previously 
described instrumental operations. 
These tests on grids have been repeated at the beginning and at the end of the work executed 
on the AP/C and once more after an intermediate phase of the experiments. Each test includes 
the plotting of two models, the first with « base in », the second with « base out ». In such a way 
we have been able to examine the whole instrumental plotting area. In table no. 1 we have 
shown the mean square deviations of the planimetric coordinates and height, and the percentage 
height error mjz . In figures 1 and 2 the results of the plotting of models 1 and 2 have been repre 
sented: in A there is the planimetric deformation of the model, in B the axonometric representation of 
the errors in height and in C the behaviour of the residual parallaxes measured on the various points. 
*) Work executed at thè « Centro di Addestramento e Studi Fotogrammetrici » of thè Politecnico 
of Milano.