Surveying and Geomatics
Surveying and Geomatics covers chain and compass surveying, levelling, theodolite and tacheometry, curves, and modern tools such as total stations and GNSS. The exam often asks for reduced levels, bearing corrections and tacheometric distances.
Core rules
- Levelling: HI=BS+RL; RL=HI−FS; arithmetic check ΣBS−ΣFS=last RL−first RL.
- Compass: magnetic bearing, true bearing, local attraction; interior angles close to (2n−4)×90°.
- Tacheometry: D=ks cos²θ+C cosθ; V=0.5ks sin2θ for a vertical staff.
- Curve: tangent length T=R tan(Δ/2); curve length L=πRΔ/180.
- GNSS gives geocentric coordinates; a total station combines EDM and angular measurement.
Worked example
A tacheometer with k=100 and C=0 has staff intercept 1.20 m at a vertical angle 10°. Horizontal distance D=100×1.20×cos²10°=120×0.9698=116.4 m. Vertical component V=0.5×100×1.20×sin20°=60×0.342=20.5 m. If instrument height and target height differ, apply the correction before reducing the level.
Traps
- Using cosθ instead of cos²θ for horizontal distance.
- Applying curvature and refraction correction with the wrong sign.
- Mixing quadrantal and whole-circle bearings.
- Forgetting the levelling-table arithmetic check.
- Treating GNSS height as reduced level without geoid correction.