Measurement and Positioning: Field Procedures and Computations
Core Concepts
Field work must be redundant, checked, and adjusted. Know traverse procedures (closed-loop and link traverses), angular closure, linear closure, precision ratios, and compass rule/Bowditch versus transit rule adjustments. Understand total station setup, backsight orientation, and resection. Know leveling (differential, trigonometric), curvature and refraction corrections, and EDM corrections for atmospheric conditions and prism constants. For GPS/GNSS, understand RTK vs. static, PDOP, fixed vs. float solutions, and coordinate systems including Arizona State Plane zones (Central, East, West) and NAD83. Know grid vs. ground distances and the combined factor.
Common Traps
Questions test whether you apply compass rule correctly (distribute misclosure proportional to course length) versus transit rule (proportional to departure and latitude). Another trap: forgetting grid-to-ground conversion - a State Plane distance is not the ground distance. Watch for angular closure tolerance expressed in seconds versus linear precision as a ratio (e.g., 1:10,000). Also be careful with azimuth vs. bearing conversions and quadrant signs.
Worked Example / Rule of Thumb
Rule of thumb: "Close your traverse; adjust by compass rule unless the problem specifies otherwise." Example: a closed traverse has a misclosure of 0.10 ft over a total perimeter of 1,000 ft. Precision = 0.10/1,000 = 1:10,000. Compass rule correction for a 200-ft course = 0.10 × (200/1,000) = 0.02 ft, applied opposite the misclosure direction. Always check that adjusted latitudes and departures sum to zero.