Survey Planning, Positioning, and Geodesy
Survey Planning, Positioning, and Geodesy
Survey planning requires defining survey objectives, area, scale, resolution, and accuracy requirements. Candidates must know how to design a survey grid (parallel lines, zig-zag, or custom) with appropriate line spacing based on the required least depth and feature detection capability. Understand positioning systems: GNSS (GPS, GLONASS, Galileo, BeiDou), DGPS, RTK, PPP, and acoustic positioning (USBL, LBL, SBL). Know geodesy fundamentals: ellipsoid, geoid, datum transformations, projections (Mercator, UTM), and coordinate systems (geographic vs projected). Be familiar with horizontal and vertical datums, geoid models (e.g., EGM96, EGM2008), and tidal datums.
Traps: Questions may ask about the spacing of survey lines for a given scale; a common rule is that line spacing should be such that the least depth is detected. For feature detection, line spacing should be no more than 3-4 times the smallest feature dimension. Another trap is datum transformation errors-always apply the correct transformation parameters. Also, GNSS height is ellipsoidal; to get orthometric height, apply the geoid separation. Be careful with projection distortions; UTM is transverse Mercator with scale factor 0.9996 at central meridian.
Rule of thumb: For a survey to detect a 2 m feature, line spacing should be ≤ 6-8 m. Worked example: If the required accuracy is 0.5 m and the GNSS baseline is 10 km, RTK may be suitable; if 50 km, use PPP or a different approach. Always verify positioning accuracy with calibration and checks.
Key terms: survey grid, line spacing, GNSS, RTK, PPP, ellipsoid, geoid, datum transformation, UTM, scale factor, geoid separation.