- 2078 Poush · 2+2 marks
Horizontal control specification for major traverse
Short answer
Major traverse uses 1''–10'' theodolite, EDM, multiple face observations, angular misclosure ≤20''√N, linear relative error 1:10,000–1:25,000, long sides >150 m, permanent stations, Bowditch adjustment. Angular accuracy is better on longer sides because fixed centering/targeting errors cause smaller angular error (≈ e/L).
Write down the general specification of horizontal control for major traverse. Why angular accuracy is better in longer side than shorter side of traverse leg?
General specification of horizontal control for a major traverse
Typical specifications adopted for a major (primary) traverse are:
| Item | Requirement |
|---|---|
| Purpose | Control framework for large projects, mapping and later minor traverses |
| Instrument | 1" to 10" theodolite; EDM or total station for lengths |
| Angle observation | Two or more sets, face left and face right, mean of both faces |
| Angular misclosure | Not more than about to ( = number of stations) |
| Linear measurement | EDM, or steel tape with corrections for temperature, tension, slope and sag, taken both ways |
| Relative closing error | 1 in 10,000 to 1 in 25,000 or better |
| Station spacing | Long sides (preferably over 150 m), adjacent sides of similar length |
| Stations | Permanent, intervisible, monumented and referenced |
| Origin | Tied to existing control stations; orientation by a known bearing or astronomical/GPS azimuth |
| Computation | Balanced by Bowditch's rule or least squares |
The exact limits depend on the specification of the controlling agency (such as the Survey Department of Nepal) for the order of the survey.
Why angular accuracy is better on longer sides
An angular error comes mainly from centering and targeting (sighting) errors, which are fixed linear amounts at the instrument station or the target, whatever the length of the line. The resulting angle error is about radians, so it becomes smaller as increases. For example, a centering error of 5 mm gives about on a 100 m side but only about on a 500 m side. Long sides therefore give better angular accuracy, while short sides should be avoided, or the instrument and targets centred with extra care (e.g. by forced centring).
✓ Answer checked by Claude Opus 5.5 (high effort)
Related questions
- Significance of traversing, accuracy parameters · Surveying II, chapter 1
- Vertical/horizontal control, stream velocity · Surveying II, chapter 1
- Link traverse Gale's table M2 to M8 · Surveying II, chapter 1
- Gale's table for traverse ABCDA · Surveying II, chapter 1
- Angular vs linear precision in traversing · Surveying II, chapter 1 · asked 2×
- Closed traverse ABCDA missing data, C(1200, 2000) · Surveying II, chapter 1
- T/F: HVDC better for longer lines · Transmission and Distribution System Design, chapter 1
- Critical position of UDL shorter than span · Theory of Structures I, chapter 5 · asked 6×
- Closed loop better than open loop (cruise) · Embedded System, chapter 7
- Preventive maintenance is better than corrective · Construction Management, chapter 9 · asked 4×