Besides performing the work of a conventional centesimal comparator for stereo 
grams and that of a conventional radial triangulator, the new instrument performs 
its primary function of a homologoscope, permitting to analogically actuate with 
geometric rigour, the identification by projection (either by pricking or by 
measuring the polar coordinates) of the pair of homologous points on the two 
conjugated linear images of a stereogram. 
The universality of the instrument develops itself both in regard to the type 
of ground photogrammetric take arrangements within the ample limits of con- 
vergency, obliquity, asymmetry, differences between the take station altitudes, 
as well as in regard to the take camera’s size. 
The theoretical schemes of the 0. M. I. Homologo-Comparator and its various 
uses are founded on the following principles, exhaustively expounded in the 
communication, namely: 
1. consideration of the take dihedral as an intrinsic geometric support of the 
reciprocal photogrammetric arrangement of the take frames made by means 
of phototheodolites; 
2. invariancy of two particular points (nuclear fulcrums) analytically identifiable 
on the two faces of the take dihedral to be considered as characteristic points 
of the reciprocal external orientation of the two frames of the photographic 
perspectives; 
3. assumption (nonessential) of a particular system of intrinsic reference of the 
numerically plotted model, bound to the take dihedral, apt to simplicity the 
plotting formulae as well as the practical execution of the plate coordinates 
measure with the homologous-comparator. 
The instrumental scheme of the Homologo-Comparator appear in the last 
analysis as a simple articulated plane system, realized in such a manner as to 
conciliate the exigencies of the photogrammetrical centesimal accuracy with 
those of the analogical operations of the projection and the intersection of the 
nuclear beams, by means of the uncoupling of the intersections similar to the 
Zeiss parallelogram system. 
The practical use of the Homologo-Comparator in synthesis consists of the 
following operations: 
1. the instrumental setting of the seven parameters of the general homographic 
plotting outline, deducable »una tantum» from the usual ones of the take 
arrangement, by means of the apposite transformation formulae; 
2. the setting of two take photograms in the apposite frames in exact internal 
orientation; 
3. the projective geometrical identification of the pair of homologs by analogi 
cal means and the successive measuring of the coordinates of each point of 
the pair to be introduced in the numerical plotting formulae. 
The primary performance as a homologoscope, typical of the instrument ren 
ders it especially suitable for plotting operations in the stereophotogrammetric 
survey of linearform material systems, such as catenary, and other suspended 
structure and also of luminous trajectories of artillery shells, bombs, missiles, 
and other moving objects in three-dimensional space (airplanes) that present 
themselves in particular, to the photographic take, as continuous uniform lines. 
The projective geometrical identification of the pair of homologs is essential 
in the case of continuous linear form objects. Where trajectories are considered 
this method frees the take from the onus of performing the synchronic accuracy 
of photographic segmentation as well as creating during the take, a pair of 
homologs which will must certainly be recognizable, which is not always possible 
in practice.