322 
  
7 og 
ze TLR Tea 
Figure 3, 
Az P,* Pr ? Fi = À* P. mA P, C =P Pr 
2 
The displacement caused by the second elevation difference would 
be: 
d = hetg(d - 8).cos 
À is the tilt of projecting beam. 
o represents the tilt of the ground feature, 
L stands for the width of the slit. 
h is for the second elevation difference. 
Note: any ground surface, tilted in the direction against the pro- 
jection center has a negtive . 
Such is the practical formula for the determination of the slit 
width. 
(3) How Much Information on Earth Needed for the Production of 
an Orthophoto map. 
When a ground surface lies in a horizontal, and parrallel to the 
photograph plane, it takes only about less than 20 bits of informa- 
tion to produce an orthophoto. When the plane is equally tilted, it 
needs several dozen of bits. To produce a 500x600mm photo map with 
the 8mm-wide slit, it takes 16K bytes of information, among which 
however there are great amount of redundancy and 2/3 or 3/4 of 
which could be dismissed by a simple reduction. It results a doubt 
in the necessity of using half-inch magnetic tapes in this case. 
(4) Integration Algorithm of "Differential Rectification”