438 
ist 
  
Observation 439 
: N 
Point in space v 
=> T Photographs 
REAL 
TIME 
Á 
Observation. 
Figure 3 
Simply put, the process involves some mathematically defined 
point in space that undergoes a transformation in order to 
position each photograph relative to an optical system viewed 
by the operator. If the system is correctly defined, the 
operator will view a stereoimage of the special object. The 
operator ‘has control over the point ‘in space and can move it 
around for the purpose of extracting data (so-called compila- 
tion). ° Orientation 9a sub-set of triangulation), on the other 
hand, 1s an inverse of this process. Here, the operator ad- 
justs the photographs to point at common images whereby the 
resulting ''measurements' are used to compute a correct 
"definition" of the photographic system. The system, there- 
fore, ‘is icompletely ‘reversible. “In fact, the process of 
"measurement for triangulation can be done on any comparator 
(not necessarily in stereo) ^and the Tesultins "definition" 
should ‘be directly applicable to ‘any’ other analytical compiler 
if there is consistency between the two systems. . The main 
point here is that in the process of triansulation (the soilu- 
tion of the measurements), the orientation of each photograph 
has been computed and should not have to be repeated in the 
compilation process. "In fact, if the trianguliation was com- 
puted for a block of pnotosraphs, the solution of the block 
System is more homogeneous than any repeated orientation of 
Ooniy two of the'photosgraphs from the block. Data from the 
block adjustment. holds for any pair of photographs from which 
an operator may want o extract data. For instance, if the 
block were made up of photography that have two-thirds for- 
ward overlap then alternate photographs could be used for data 
extraction with no loss. dn accuracy of the orientation process! 
In fact, the compilation process should be more accurate since 
the operator is now working with photography with a greater 
base-height ratio. To repeat, the procedure is feasible only 
if all the processes are consistent. 
Where in the process shouid one first concentrate on stand- 
ardization? | An expansion on that part of the proceding figure 
$ that. depicts object. space might help. to answer. this question. 
Figure 4 brings out the fact, that, most, applications cf photo- 
grammetry are concerned with mapping the earth's surface which 
is a curved figure. | Geodesists have chosen to describe the 
positions-of^points on the earth's surface with curvilinear