322 323 
An orthophoto making process is similar to plotting "random curves" 
in a five-dimentional space. A fine image can be achieved by smooth 
and accurate plotting of these "random curves". (see Figure 4). 
  
Figure 4. 
A random curve is divided into numerous pieces and every piece can 
be represented by a straight line. For each piece of the line the 
slops are to be computed, namely: dx/dt, dy/dt, dY/dt, dX/dt and 
dm/dt, in which only dY/dt is a constant. When dY/dt=1, it is 
treated as an undivided frequency; when avy/at='/2, it is regarded 
°C) = 
as half frequency. Frequency division is aimed at uniforming the 
pulses; and the orthophoto process is more or less like running 
integrstor. 
m (di qt = 127 
x = [dx dt , y 7 lat dt * 2958 2229 
A pulse would be transmitted to a degree of freedom, whenever an 
integrated value exceeds an integral. In this way, a five-dimen- 
tional curve can be "plotted” out. 
ma (5) Correction of Optic-Mechanical Errors by a Program. 
it 
Eh The manufacture accuracy is limited, but the computation accuracy 
A becomes more and more precise with the expanding of the word length. 
Using program to correct optic-mechanical errors caused by manufac- 
‚bt 
turing is the common practice and charicteristics in modern instru- 
ments. 
In modern precise photogrammetric instrument, software plays a