that the local Cartesian system is oriented in such a way that the (x) (Y) 
plane is normal to the plumb line direction at the center of projection and 
35) further assuming that refraction acts only on the elevation angle, 
tangent to light curve 
*(Z) 
s: 
E 
) 
86 ' L-curve of light ray 
t 
Los (xyz) 
v 
$ 8 (Z) 
A 
Y 
(x Y 2) a HX) 
87) NU 
\ 
is 
x ) 
\ 
SN 
+(Y) v 
Mv 
v 
\ 
\ 
it 
Figure 10 
à 
1las 
1g 
55