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When the base of the object is accessible Calculate the R.L of B, if D = 24.96 m, angle for line of sight is +4ᶿ24ᶿ, height of the axis will be 1.29 m and the R.L of A is 400 m.
403.21 m
430.21 m
403.12 m
401.32 m
403.21 m
Given: Distance D = 24.96 m, Angle of elevation θ = 4°24', Height of instrument axis h = 1.29 m, R.L of instrument station A = 400 m
Distance D = 24.96 m, Angle of elevation θ = 4°24', Height of instrument axis h = 1.29 m, R.L of instrument station A = 400 m
R.L of B=R.L of A+h+Dtanθ
Convert Angle to Decimal Degrees
Convert angle θ=4°24′ into decimal degrees by dividing minutes by 60.
θ=4+6024=4.4°
Calculate Vertical Height (V)
Using trigonometrical levelling for an accessible base, vertical elevation V=Dtanθ.
V=24.96×tan(4.4°)=24.96×0.0769=1.92 m
Calculate R.L of Point B
Add instrument height h and vertical elevation V to the R.L of station A.
R.L of B=400+1.29+1.92=403.21 m
A is correct because the calculated Reduced Level of point B is exactly 403.21 m.
When the base of the object is inaccessible, two instrument stations are used and simultaneous equations involving instrument heights are solved to find the R.L.