Surveying Instrumentation and Field Procedures
This domain tests equipment selection, instrument checks and adjustments, and the field procedures that keep a survey defensible. Expect questions on collimation and two-peg tests, face-left and face-right observations, prism constants, GNSS RTK setup, and traverse procedure.
Instruments and routine checks
- Total station: check plate and circular levels, optical plummet or laser plummet, horizontal and vertical collimation, trunnion axis, compensator, and the EDM additive constant. Confirm the prism constant in the instrument matches the prism in use.
- Levels: perform a two-peg test to detect collimation error; check the compensator by tapping near the instrument and confirming the reading settles; check the rod for zero error and foot wear.
- GNSS RTK: verify the base position and coordinate, check PDOP and multipath environment, confirm initialization, and shoot known control points as check shots before accepting any new point.
- Traverse: close the horizon at each setup, use face left and face right (double centering) to cancel instrument errors, center carefully over the mark, and record the raw observations, not just computed values.
Worked example: two-peg test
Set pegs A and B 60 m apart and set the level exactly midway. Readings: A = 1.500, B = 1.400, so the true height difference is 0.100 m with B higher, because equal sight lengths cancel collimation error. Move the instrument to 3 m from A. Readings: A = 1.550, B = 1.490. If the line of sight were correct, B would read 1.550 - 0.100 = 1.450. It reads 0.040 m high over about 57 m, roughly 0.7 mm per meter, so the line of sight is rising and the crosshair or compensator needs adjustment. Until it is adjusted, either balance sight lengths closely or apply a correction proportional to sight distance.
Traps that cost marks
Believing balanced sight lengths cancel every error; they do not cancel rod scale error or refraction gradients. Using a prism constant from a different prism model. Skipping check shots on RTK work so a bad base position propagates silently. Accepting a traverse because linear closure looks good while the angular misclosure is large. Recording angles to fewer significant figures than the instrument displays. Failing to note occupation evidence and weather in the field book.
Documentation
Field notes should carry the date, personnel, instrument and serial number, weather, sketch, ties to permanent features, and the disposition of every monument found, set, or not found. Notes are evidence and may be examined years later, so write them as though a stranger must reproduce your work.