200 
developments) and the challenge of outer space provided the stimulai while 
technological advancements cohtinued to provide the necessary support. 
Furthermore, at the beginning of this period, the basic principles 
of statistics were no novelty to the photogrammetrist. The theory of 
errors and the method of least squares had served him well. However, at 
this stage more and more people started to realize that the modern stat 
istical principles would show how to improve the reliability of various 
minor operations, analogic or analytic. They even started to realize as 
to how to plan a job to obtain the maximum amount of information from the 
number of observations which one can afford to make (due to economic and 
time considerations) and how to determine the reliability of inference 
from them. 
The units to measure distances remained an unresolved entity to 
the photogrammetrists. Centuries ago, a foot was defined as. the length of 
06 barley grains strung end to end and the yard was the distance from the 
tip of King Edgar's nose to the end of his outstretched hand. Since then 
we have come a long way. The yard is now measured in terms of the wave 
length of light and time by the duration of atomic vibration. However a 
confusion did exist internationally, particularly between the two major 
systems: CGS (Centimeter-Gram-Second) and FPS (Foot-Pound-Second). The 
CGS system with two variations devised by European Scientists in the 1800s 
was unified in the early 20 th century into the MKS (Meter-Kilogram-Second) 
system. Then in 1954, at the X General Conference of Weights and Measures 
held at Sèvres, France the Ampere (A) being chosen as the fourth base 
unit, this system was referred to as the MKSA system. Finally in 1960 at 
the XI General Conference of Weights and Measures, the system of units 
proposed in 1954 was officially entitled "Système International d'unités" 
with its abbreviation being SI. This being a coherent system, it is now 
used by over 80 per cent of the people of the world. Although ISPRS en 
courages this system, its full official implementation encounters diffi 
culties.. 
As with the units (meter, foot, etc.), there existed a confusing 
multitude of systems of coordinates. After numerous deliberations finally 
an International System of Coordinates (Ghosh 1988) was accepted in 1956 
(ISP Archives, 1956 and 1960 Congresses). Its universal implementation, 
however, remains yet to be fulfilled. 
In view of computational-analytical approaches, the photogram 
metrist started to understand in the early 1950s the necessity and import 
ance of items like "random sampling", "test of hypotheses" or "degrees of 
freedom" at even minor stages of operations involving also such effects as 
film shrinkage, lens distortion or temperature variation. Questions re 
lated to consideration of for example "weight" and "correlation", "obser 
vation equations" against "condition equations" or "observations" against 
"quasi-observations" started to be raised in the computational approaches. 
Practically all of such developments are recorded in numerous 
publications around the world. Thus, before drawing our attention here to 
the specific developments, it would be appropriate to identify the most 
significant publications or information sources in this regaid.