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🔗 Closed Traverse
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Field Checklist (Supervisor-Free)
Stop Rules
- Cannot prove control reliability OR coordinate system/UTM zone is uncertain
- Angular misclosure exceeds ±1'√n after re-observation
- Linear precision worse than 1:1000 after re-checks (Basak: reject)
- A single leg correction > 3× average and no field cause found (blunder likely)
- Backsight/orientation is unstable (backsight point moved/unclear)
- Intervisibility breaks and stations are improvised without re-planning
STEP 1
Reconnaissance
STEP 1 — RECONNAISSANCE (FIELD SOP) Goal: design a traverse that can be observed cleanly, checked on-site, and will close. Minimum equipment (trainee-safe): • Total station + tribrach + tripod (spikes working) • Prism + pole + bipod (stable) • Plumb bob / optical plummet, rod bubble • Pegs/nails/paint + hammer + marker • Field book (or METARDU Field Mode) + backup pen • Tape (for short ties), machete/brush cutter if needed • PPE: boots, vest, helmet if construction site Recon rules (do NOT skip): 1) Walk the whole polygon route. 2) Confirm intervisibility: every station must see the next AND previous station. 3) Choose stable stations: firm ground, not loose soil, not on traffic/vibration, not on manhole covers. 4) Avoid bad geometry: very short legs mixed with very long legs; keep legs “reasonable” and balanced. 5) Plan closure: close back to start OR to a different known control point (preferred for a stronger check). 6) Identify recovery: record a witness tie for each station (e.g., “0.80 m to tree”, “1.20 m to wall corner”). Booking template (copy into field book): Station | BS To | FS To | FL Angle | FR Angle | Slope Dist | Vert Angle | HI | HR | Notes Check: Σ(angles) vs theoretical, and note any repeats/rejections. Trainee “stop gate” during recon: If you cannot guarantee intervisibility and a realistic closure plan, STOP and redesign stations before observing.
STEP 2
Establish Control
STEP 2 — ESTABLISH CONTROL (FIELD SOP) Control is the foundation. If control is wrong, every coordinate you produce is wrong. Minimum control requirement (trainee-safe): • At least TWO known points (different coordinates) • Their IDs must match what is on the ground (beacon ID / BM name / peg label) • Your project coordinate system must be explicit: UTM zone + hemisphere + datum (WGS84/Local) Control verification procedure: 1) Recover control physically (find the mark, not just “near it”). 2) Photograph the mark and its surroundings. 3) Take a short witness tie (offsets to nearby permanent features). 4) Check the control pair: • Measure distance and bearing between the two control points (one quick setup is enough). • If the measured check is inconsistent with expected values (or differs unreasonably), STOP. If control comes from GNSS today: • Confirm fix quality (RTK FIX vs FLOAT), PDOP, and occupation time. • Re-observe at least once (repeat occupation) if the job is cadastral/engineering. METARDU setup: → Project Settings: confirm UTM zone + hemisphere → Add both control points as Primary Control → Lock them (prevents accidental edits) Trainee stop gate: If you cannot state the control source, datum, and verification check you performed, STOP.
STEP 3
Set Up Instrument
STEP 3 — SET UP INSTRUMENT (FIELD SOP) Objective: occupy the correct station, centered and leveled, with known HI/HR and correct EDM settings. Setup sequence (do in this order): 1) Tripod: legs firm, head roughly level, station mark centered under head. 2) Mount instrument + tribrach; lock lightly. 3) Centering: optical plummet/plumb bob to station mark (fine adjust). 4) Leveling: circular bubble → plate bubble → electronic level (fine). 5) Re-check centering AFTER leveling (leveling often shifts centering). 6) Record HI (instrument height) to 0.001 m if possible. 7) Prism: confirm HR (prism height), prism constant, and target type. 8) Instrument settings: units = meters; angles = DMS; EDM mode correct (prism/reflectorless); apply met corrections if used. Quick “orientation sanity” before observing: • Sight the backsight point. Confirm the point ID and that it is stable. • Set/record your reference: either set Hz = 0°00'00" on backsight OR record the backsight bearing explicitly. Trainee stop gate: If you cannot keep the bubble centered through a full rotation, or centering keeps drifting, STOP (tripod not stable / legs sinking).
STEP 4
Measure Observations
STEP 4 — MEASURE OBSERVATIONS (FIELD SOP) At every station, your job is to produce reliable angles + distances with redundancy. Station observing pattern (recommended): 1) Set up on station i (HI recorded). 2) Backsight to station i−1 (confirm ID). Set Hz reference (0°00'00") OR record the backsight bearing. 3) Foresight to station i+1 (confirm ID). Observe: • Horizontal angle • Distance (prefer horizontal distance; if slope distance is recorded, record vertical angle too) 4) Repeat as a set: • Face Left (FL) + Face Right (FR), or two full sets if instrument is simple. Distance handling (trainee-safe): • If your total station shows BOTH slope and horizontal distance, book the horizontal distance for traverse. • If you only have slope distance, you MUST record vertical angle and reduce to horizontal (do not ignore). Field tolerances (set your job tolerance before starting): • FL vs FR angle difference: re-observe if outside your tolerance (example: 20″). • Distance repeats: re-measure if outside instrument spec (example: > (2 mm + 2 ppm × D)). • If backsight is disturbed (person kicks peg / prism moved), redo the station immediately. Angular check (do this BEFORE leaving site): • If you observed included angles for an n-sided closed traverse: Theoretical sum = (n − 2) × 180° Allowable misclosure (Basak) = ±1' √n • If the misclosure exceeds the limit: find the problem station and re-observe (do not wait for office). METARDU entry tip: If you enter bearings/distances (instead of raw angles), ensure your bearings are Whole Circle Bearings (0–360°) and consistent with your backsight reference.
STEP 5
Compute Traverse
STEP 5 — COMPUTE + QUALITY CHECK (FIELD/Office SOP) METARDU computes the traverse and tells you whether it is acceptable. METARDU computes: ✓ Latitude/Departure per leg (Lat = D×cos(WCB), Dep = D×sin(WCB)) ✓ Closing error (ΔE, ΔN) and linear misclosure ✓ Relative precision ratio (Total traverse length / Misclosure) ✓ Bowditch corrections per Basak: corrE = -(legD/totalD) × closingErrorE corrN = -(legD/totalD) × closingErrorN ✓ Adjusted coordinates + Gale’s Table output Acceptance gates (Basak): • Urban cadastral: ≥ 1:5000 • Suburban: ≥ 1:3000 • Rural: ≥ 1:1000 If precision is POOR (trainee workflow): 1) Check for “obvious” blunders: • Wrong station ID / swapped from-to • Wrong face reading typed • Wrong HI/HR or prism constant • Decimal point error on distance 2) Look at corrections per leg: • If one leg correction is > 3× average, suspect that leg first. 3) Re-observe the suspect station/leg immediately (best), then re-run. Hard stop rules: • Precision < 1:1000 after re-observation → reject and redesign/re-observe. • Angular check exceeds ±1'√n and cannot be isolated → re-observe angles. • Closing to a known point fails significantly (link traverse) → control or orientation problem.
STEP 6
Generate Report
STEP 6 — DELIVERABLES + HANDOVER (SOP) Before you “finish the job”, make the work defendable. In METARDU: → Generate Report (PDF) Minimum deliverables for a closed traverse job: • Control point list (names, coordinates, datum/UTM zone) • Raw observations summary (angles/distances, sets count) • Misclosure values (ΔE, ΔN, linear) + precision ratio + grade • Adjustment method stated (Bowditch) + per-leg corrections • Final adjusted coordinates table • Diagram/sketch reference (station descriptions + witness ties) Trainee rule: Never discard raw field notes. If a coordinate is challenged later, raw notes are your evidence.