Surveying, Geomatics and Remote Sensing Applications
Questions are traditional plus modern: chain and compass work, levelling, theodolite and tacheometry, then geomatics - GPS, remote sensing and GIS. Conceptual items on resolution and map projections are as likely as reduction-of-levels arithmetic.
Core rules
- True bearing = magnetic bearing ± declination; east declination is additive, west subtractive.
- In a closed traverse, Σ interior angles = (2n − 4) × 90°; closing error is distributed by the Bowditch rule when linear measurements are of comparable precision.
- Height of instrument method: HI = RL of benchmark + backsight; RL = HI − intermediate sight or foresight. Check: ΣBS − ΣFS = last RL − first RL.
- Curvature and refraction correction is 0.0673 D² (D in km), always subtractive.
- Anallatic tacheometry: D = 100 s cos²θ + C cosθ.
- GPS has space, control and user segments; a fix needs four satellites because receiver clock bias is an unknown.
- Remote sensing resolutions are spatial, spectral, radiometric and temporal; NDVI = (NIR − Red)/(NIR + Red).
Worked example
Level book: backsight 1.585 on a benchmark of RL 100.000 gives HI = 101.585. An intermediate sight of 2.105 gives RL 99.480; a foresight of 1.925 gives RL 99.660. Check: ΣBS − ΣFS = 1.585 − 1.925 = −0.340, and 99.660 − 100.000 = −0.340. Agreement confirms the reduction.
Traps
Adding a west declination instead of subtracting it; using D in metres rather than kilometres in the curvature correction; forgetting that refraction is about one-seventh of curvature and reduces the total correction; and confusing LISS-IV's 5.8 m resolution with Cartosat's finer PAN data.