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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{cosα–(2θ – γ ) sinα}

Z = L{sinα+(θ – γ ) cosα}

θ = L.cosα/2R........... Earth curvature

correcting item

γ =K

•

Lcosα/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

•

cosα

Z=L

•

sinα

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”.

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Topcon GTS-823A Manuale Utente Pagina 122