2.3. Application programs 
  
The application programs of an analytical instrument are the 
real-time, near-real-time and off-line programs that comprise the soft- 
ware for control of positioning devices and the actual photogrammetric 
data processing. Writing of these programs on contemporary mini- 
computers is considerably simplified by the software operating systems 
that were outlined in 2.1. From the functional point of view, applica- 
tion programs may be divided into two groups. In one group belong the 
programs that are needed for determination of parameters, leading to 
the reconstruction of oriented stereomodels (e.g. interior, relative, 
absolute or simultaneous outer orientation), and in the other group the 
programs needed for collection and processing of data from an oriented 
model (e.g. digitizing, graphical plotting, scanning). For convenience 
one can call them orientation programs and compilation programs. The 
programs from both groups may have parts that have to be written for 
real-time, near-real-time or off-line operations. 
The separation of programs into real-time, near-real-time and 
off-line is not very practical because the overall dynamic operations 
of an analytical instrument is a result of the interaction of these 
three types. The real-time parts of programs are normally operating in 
a deterministic manner while the others normally involve a stochastic 
model. For example, each orientation program will have an initialiser 
that is an on-line, near-real-time program usually written in a conver- 
sational mode. This part of the orientation program will prompt the 
operator to introduce the data necessary for the particular operation 
(e.g. constants, limits), and to indicate the manner in which the opera- 
tion should be performed (e.g. choice of parameters to be determined by 
relative orientation program). It will at the same time check if all 
the information needed for the continuation of the indicated operation 
is available (e.g. it will not permit the execution of a subsequent 
computational step in the process if any necessary information is 
missing). The next operation in an orientation program is normally a 
data collection procedure (e.g. measurement of photo-coordinates or 
parallaxes) controlled by an on-line, real-time part of the orientation 
program. After the completion of that step, the actual adjustments and 
determination of parameters will take place in an off-line mode, provi- 
ded that a check on the collected data confirms that its number and 
quality is satisfactory. In this part the operator does not have a 
direct control over the processes, except in case of malfunction (e.g. 
slow convergency). Although, if so desired, the operator may be able 
to inspect the intermediate results and monitor the operation. 
The compilation programs have in general as their core a basic 
real-time program that controls, according to a chosen mathematical 
model, the basic functional relationship between the model and image 
coordinates, and corrects for all defined systematic errors. The role 
of a correction routine in a basic real-time program is to ensure the 
addressing of the real position of the image point, since the image 
coordinates obtained by the transformation according to the determinis- 
tic mathematical model would address the location where that point 
should be if the acquisition and measurement of data was free of 
Systematic errors. Thus the correction routine in basic real-time 
programs may be thought of as the inverse of the correction routine in 
orientation programs. Besides the basic real-time part, a compilation