(394) 
increasing errors have to be taken into account when matching a great number 
of models. There is now a tendency to employ algebraic methods, vertical paral- 
laxes are measured by figures and one tries to get the correction values of 
orientation elements by extremely refined calculating methods. The computed 
values are set on the circles of the instruments but inspite of correct measuring 
and calculating slight residual vertical parallaxes usually remain. These residual 
parallaxes have at last yet to be eliminated by the optical-mechanical method. 
This fact seems to be due to instrumental influences. 
1). The divisions of the circles on most of the instruments are not suffi- 
ciently accurate to obtain the necessary accuracy of 0,5 minutes for setting the 
computed values of orientation elements. 
2). Even if the correct values had been set on the corresponding circles 
the effect on the plotting system is probably not wholly accurate, this seems to 
be due to the influence of instrumental errors as explained by O.v. Gruber 2) 
for the Stereoplanigraph and Wild Autograph. 
In order to avoid the mentioned influences the computing method has been 
extended, one transfers also by calculating the improvements of orientation to 
the model ie. the plotting system especially by calculating hight differences 
caused by the improvements of orientation. Thus the correct heights of model 
are obtained and subsequently the elements of orientation changed to such 
extent, that the floating mark gives also these correct heights. Of course this 
extended computing methed is too time-consuming for most practical purposes 
and can be employed easily only for getting tilt-corrections using the vertical 
epipolar planes as has done Schroeder ?). 
The optical-mechanical method is not hampered by instrumental error 
influences, at least as regards the intersection of rays in space and the elimina- 
tion of vertical parallaxes. As Kasper *) has proved it is the best, most accurate 
and quickest method for getting final correct relative orientation. 
In the future new instruments for instance the stereoplanigraph C-8 offers 
the possibility for setting very accurately the elements of orientation and also 
for reading the values of these elements very clearely and comfortably. That is 
a quite remarkable new arrangement. In this manner the influence 1) seems to 
be reduced to a sufficient degree, further experience will have to show whether 
also the influence 2) exists or not. In any case computing methods for orientation 
will be stimulated by the new arrangement. It is not yet certain whether final 
improvements of orientation by the optical-mechanical method will still be 
necessary. 
I he influence of instrument-scale. 
In this connection an experience may be communicated which concern also 
the error influences of instrument and the most favorable choice of instrument- 
scale. This experience was made when plotting photographs for cadastral work 
?) Gruber, O. von, Ferienkurs in Photogrammetrie p. 399 and 413, Stuttgart 1930, also R. Fin- 
sterwalder, Photogrammetrie. Berlin 1952 p. 219 and 223-225. 
3) Schróder, F. Ein Beitrag zur rechnerischen Orientierung von Bildpaaren. Allg. Verm. 
Nachr. 1952, Heft 9, S. 201-208. 
^) Kasper, H. Essais effectués à l'autographe Wild A5 en vue d’etablir la précision et le rende- 
ment de quelques nouveaux procédés d'orientation relative pour des levés verticaux. Bull. de 
la Soc. Belge de Photogrammetrie 1950/51.