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.