Topcon AP-L1A - 12 Correction for Refraction and Earth Curvature; Distance Calculation Formula

12. CORRECTION FOR REFRACTION AND EARTH CURVATURE
12-1
12. CORRECTION FOR REFRACTION AND EARTH
CURVATURE
AP-L1A series measures distance, taking into account correction for refraction and earth curvature.
Note : If the telescope is positioned within  9C from the nadir or zenith, no measurement will
result even if the correction function for refraction and earth curvature works.
The display shows “W/C OVER".
12.1 Distance Calculation Formula
Distance Calculation Formula; with correction for refraction and earth curvature taken into account.
Follow the Formula below for the converting horizontal and vertical distances.
Horizontal distance D=AC(

) or BE(

)
Vertical distance Z =BC(

) or EA(

)
D=L{cos

-(2 -

)sin

}
Z=L{sin

-( -

)cos

}
=Lcos

/2R ......... Earth curvature
correcting item

=KLcos

/2R ...... Atmospheric
refraction
correcting item
K=0.14 or 0.2 ....... Coefficient of
refraction
R=6372km ............ Radius of earth

( or

) ................. Altitude angle
L ............................ Slope distance
 The conversion formula for horizontal and vertical distances is as follows when correction for
refraction and earth curvature is not applied.
D = Lcos 
Z = Lsin 
Note : The coefficient of AP-L1A has been set at 0.14 before shipment (K=0.14).
if the "K" value is to be changed, refer to "16. Selecting mode".
Radius of esrth
R = 6372 Km
E
D
C
B
A
-Z
20
20
0



2