27. EXPLANATIONS
152
The instrument measures distance, taking into account correction for refraction and earth curvature.
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
)
Vertical distance Z = BC(
α
)
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
g = K
•
Lcos
α
/2R : Atmospheric refraction correcting item
K = 0.142 or 0.2
: Coefficient of refraction
R = 6371km
: Radius of earth
a
: Altitude angle
L
: Slope distance
Changing "K (Coefficient of refraction)" value : "20.1 Observation Conditions"
27.2
Correction for Refraction and Earth Curvature
Radius of earth
R=6371km
