Topcon GTS-823A - Manual (Page 122)

12-1
12 CORRECTION FOR REFRACTION AND EARTH CURVATURE
12 CORRECTION FOR REFRACTION AND EARTH
CURVATURE
The instrument measures distance, taking into account correction for refraction and earth curvature.
12.1 Distance Calculation Formula
Distance Calculation Formula; with correction for refraction and earth curvature taken into account.
Follow the Formula below for converting horizontal and vertical distances.
Horizontal distance D = AC( α ) or BE( β )
Vertical distance Z =BC( α ) or EA( β )
D = L{cos α –(2 θ – γ ) sin α }
Z = L{sin α +( θ – γ ) cos α }
θ = L.cos α /2R........... Earth curvature
correcting item
γ =K • Lcos α /2R....... Atmospheric
refraction
correcting item
K =0.14 or 0.2.......... Coefficient of
refraction
R =6372km.............. Radius of earth
α ( or β )................... Altitude angle
L .............................. Slope distance
l The conversion formula for horizontal and vertical distances is as follows when correction for
refraction and earth curvature is not applied.
D=L
• cos α
Z=L • sin α
Note: The coefficient of the instrument has been set at 0.14 before shipment (K=0.14).
if the "K" value is to be changed, refer to 8 “PARAMETERS SETTING MODE”.
Note: If the telescope is positioned within ±9° 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”.