--- title: "Horizontal control specification for major traverse" subject: "Surveying II" chapter: 1 key: "semester_4/surveying_ii:traverse-horizontal-control-specification" source: https://www.bctengineer.com/q/semester_4/surveying_ii/traverse-horizontal-control-specification site: BCT Engineering --- # Horizontal control specification for major traverse Surveying II · Chapter 1: Traversing - Asked in: 2078 Poush, 2+2 marks - Video: [Specification of Horizontal and Vertical control points | Lecture:2 | Surveying 2nd | Prashant YT |](https://www.youtube.com/watch?v=H-WurIVyN8I) — Prashant YT - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_4/surveying_ii/traverse-horizontal-control-specification - Whole chapter: https://www.bctengineer.com/md/semester_4/surveying_ii/chapter-1 ## Question 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? ## 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). ## Answer #### 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 $10''\sqrt{N}$ to $20''\sqrt{N}$ ($N$ = 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 $e$ at the instrument station or the target, whatever the length of the line. The resulting angle error is about $e/L$ radians, so it becomes smaller as $L$ increases. For example, a centering error of 5 mm gives about $10''$ on a 100 m side but only about $2''$ 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). ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. How are angles observed in a major traverse? A. A single face left reading B. Two or more sets on both faces, taking the mean C. By compass only D. One set, face right only Answer: B. Both faces cancel instrumental errors, and several sets improve precision. (Key point: Angle observation) 2. What relative closing error is typical for a major traverse? A. 1 in 10,000 to 1 in 25,000 or better B. 1 in 500 C. 1 in 1000 D. 1 in 3000 only Answer: A. Major control traverses require high precision, far stricter than minor traverses (1 in 3000 to 5000). (Key point: Relative closing error) 3. Why is angular accuracy better on longer sides? A. Longer sides have larger centering errors B. Angles are measured more times on longer sides C. Longer sides need a lower-grade instrument D. Centering and targeting errors are fixed linear amounts e, so the angle error e/L is smaller for large L Answer: D. Angular error = e/L radians, which decreases as L increases. (Key point: Why long sides better) 4. Which station spacing is recommended for a major traverse? A. Very short sides to increase checks B. Sides of widely different lengths C. Long sides (preferably over 150 m) with adjacent sides of similar length D. Sides under 30 m Answer: C. Long, similar sides reduce the effect of centering errors on angles. 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