Technology - GATE GE (Geomatics Engineering)
The Technology domain tests the sensors, platforms, and digital processing used to acquire and manage geospatial data: GNSS, remote sensing, LiDAR, photogrammetry, and GIS. Questions favour working formulas, resolution trade-offs, and processing logic over product names.
Core rules and concepts
- GNSS pseudorange positioning reaches metre-level; carrier-phase positioning reaches centimetre-level but requires ambiguity resolution. RTK needs a base station or network correction.
- PDOP describes satellite geometry; a low PDOP indicates better geometry.
- Remote sensing has four resolutions: spatial, spectral, radiometric, and temporal.
- Photogrammetric ground sample distance is GSD = H × p / f, where H is flying height above ground, p is pixel pitch, and f is focal length.
- LiDAR point density depends on pulse repetition frequency, scan angle, and flying speed.
- GIS distinguishes raster and vector models; topology governs adjacency and connectivity.
Worked example
An aerial camera has f = 100 mm, pixel pitch p = 10 µm, and flying height H = 2000 m above ground. GSD = 2000 × 0.00001 / 0.1 = 0.2 m. The reasoning is similar triangles: the ground footprint of one pixel scales with height and pixel size, and inversely with focal length. Convert all lengths to metres before dividing.
Traps that cost marks
- Confusing GSD with map scale; they are different quantities.
- Ignoring terrain relief when quoting a single GSD.
- Assuming RTK works without a base or network correction.
- Mixing radiometric resolution with spatial resolution.
- Applying NDVI to a panchromatic image, which lacks the required NIR and red bands.