SHANGHAI ESURVEY GNSS CO., LTD.
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Horizontal axis: the measured temperature.
Vertical axis: the pressure.
Diagonal line: the required atmospheric correction value.
8.2 Correction for Refraction and Earth Curvature
Considering the correction of refraction and earth curvature for distance measurement, the
formula for slope distance, horizontal distance and vertical distance applied in the
instrument are as followings:
SD = D
o
* (1 + ppm *10
-6
) + mm
o SD: displayed slope distance (m)
o D
o
: real measured distance (m)
o ppm: scale coefficient (mm/km)
o mm: target constant (mm)
HD = Y - A * X * Y; VD = X + B * Y
2
o HD: horizontal distance (mm)
o VD: vertical distance (mm)
o Y: SD * |Sin|ξ (ξ: zenith angle)
o X: SD * Cosξ (ξ: zenith angle)
o A: (1 - K / 2) / R (K = 0.142 or 0.20; R = 6.37 * 10
6
) (m)
o B: (1 - K / 2) / 2R (K = 0.142 or 0.20; R = 6.37 * 10
6
) (m)
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