Leveling & Vertical Control
PublicDifferential leveling procedures, errors, and accuracy standards for vertical control surveys
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Cards (8)
What is the basic leveling equation?
Elevation B = Elevation A + BS - FS Or: HI = Elev A + BS Elev B = HI - FS — Ghilani Elementary Ch. 4
What is the curvature and refraction formula?
c + r = 0.067 D² meters (D in km) c + r = 0.021 M² feet (M in miles) Always makes rod reading TOO HIGH. Eliminate by balancing BS and FS distances. — Ghilani Elementary Ch. 4
What are the leveling accuracy standards?
First-Order Class I: 3 mm √K First-Order Class II: 4 mm √K Second-Order Class I: 6 mm √K Second-Order Class II: 8 mm √K Third-Order: 12 mm √K (K = distance in km) — FGDC Standards
Why balance BS and FS distances?
Balancing ELIMINATES: 1. Collimation error 2. Curvature effect 3. Refraction effect All are proportional to distance; if BS ≈ FS, they cancel. — NOAA NOS NGS-3
What is the peg test?
A field test for COLLIMATION ERROR: 1. Set two points ~200 ft apart 2. Level midway, read both 3. Level near one point, read both 4. Compare ΔH values If different, collimation error exists. — Ghilani Elementary Ch. 4
What is reciprocal leveling?
For crossing OBSTACLES where distances can't be balanced: 1. Set up on side A, read A and B 2. Set up on side B, read B and A 3. Average the two ΔH values Systematic errors cancel in the mean. — Ghilani Elementary Ch. 4
How do you adjust a level loop?
Proportionally by distance: Correction at TP = -(misclosure × cumulative distance / total distance) ONLY adjust if closure is within tolerance! — Ghilani Elementary Ch. 4
What is trigonometric leveling?
ΔH = S × sin(α) + hi - ht Or: ΔH = HD × tan(α) + hi - ht Where: S = slope distance α = vertical angle hi = instrument height ht = target height Apply c+r for long distances. — Ghilani Elementary Ch. 4