Surveying and Geomatics
Surveying and Geomatics covers chain and compass surveying, levelling, theodolite traversing, curves, triangulation, GPS, GIS, and remote sensing. The exam tests field procedures, reductions, and error corrections.
Core rules
- Height of instrument (HI) = RL of BM + backsight; RL of a point = HI − foresight.
- In a closed traverse, the algebraic sum of latitudes and departures should be zero; closing error is adjusted by Bowditch's rule for compass traverses.
- True bearing = magnetic bearing ± magnetic declination; add east declination, subtract west.
- Curvature and refraction correction is approximately 0.0673D² m, with D in km.
- GPS uses trilateration from satellites; GIS links spatial features to attribute data.
Worked example
A backsight of 1.500 m is taken on a benchmark of RL 100.000 m. HI = 100.000 + 1.500 = 101.500 m. A foresight of 2.200 m to a station gives RL = 101.500 − 2.200 = 99.300 m. In the rise-and-fall method, the same result is a fall of 0.700 m from the BM, confirming the arithmetic.
Traps that cost marks
- Adding a foresight instead of subtracting it.
- Applying declination in the wrong direction.
- Ignoring curvature and refraction for long sights.
- Confusing face-left and face-right readings in theodolite work.
- Misapplying Bowditch's rule to a traverse with large angular error.
Exam focus
Practise level-book reductions, bearing conversions, traverse adjustments, and simple horizontal-curve elements.