Setting Out
Core concepts
Setting out transfers design positions to the ground. Know the methods for setting out a building: 3-4-5 method (Pythagoras), offset method, and theodolite method. For curves, learn simple circular curves, their elements (tangent length, curve length, external distance, mid-ordinate, chord), and the setting-out methods: offsets from the long chord, offsets from the tangent, and rankine's deflection angle method.
Understand setting out for sewers (gradient, invert level, sight rails, boning rods), for roads (centre line, formation level, side slopes), and for pipelines. Learn the terms: base line, reference points, pegs, and check measurements.
Traps in questions
- For a simple curve, tangent length T = R tan(Δ/2); length of curve L = RΔ (Δ in radians) or πRΔ/180.
- The 3-4-5 triangle gives a right angle; a 5-12-13 triangle is also valid.
- Setting out a sewer: invert level = formation level − diameter; gradient = fall per unit length.
- Sight rails are set at a fixed height above the invert; boning rods transfer the line.
- Deflection angle method uses the formula δ = 1719 × C / R (δ in minutes, C = chord in m).
Worked example / rule of thumb
A curve with R = 200 m and Δ = 30°: T = 200 tan 15° = 200 × 0.2679 = 53.59 m; L = π × 200 × 30/180 = 104.72 m. Rule: always convert Δ to radians for L = RΔ.
For a sewer with a fall of 1 in 100 over 50 m, the total fall = 0.50 m. If the invert at the start is 10.00 m, the invert at the end is 9.50 m.
Survey Records
Core concepts
Survey records are the documentary evidence of field work. Know the types: field book (chain, level, theodolite), level book (reduced level register), traverse sheet, computation sheets, and the survey report. Understand what each must contain: date, weather, instrument, observer, station, readings, and remarks.
Learn the rules for recording: entries in ink, no erasures (strike through and initial), sequential numbering, and sketches to supplement numbers. Understand the difference between field notes (raw) and computed results (processed).
Traps in questions
- Never erase; strike out with a single line and initial the correction.
- Record the reading as observed; corrections belong in the computation, not the field book.
- Level book: BS, IS, FS columns with HI and RL; the arithmetic check must be shown.
- Sketches are essential for tie lines and offsets; they must be to a stated scale.
- The survey report summarises purpose, method, results, and limitations.
Worked example / rule of thumb
A level book page has BS 1.50, IS 1.70, FS 1.80. The arithmetic check: ΣBS − ΣFS = Σ rises − Σ falls = last RL − first RL. Show all three columns; a mismatch signals a recording error.
Rule: if it is not recorded, it did not happen. Field notes must allow a second person to recompute the results without seeing the site.
Drafting and Professional Practice
Core concepts
Drafting converts survey data into maps and plans. Know the scales (representative fraction, graphical scale), the conventional symbols, the north point, the title block, and the legend. Understand the difference between a map (small scale, large area) and a plan (large scale, small area).
Learn the drawing standards: line weights, lettering, dimensioning, and the layout of a drawing sheet. Understand the professional practice: the surveyor's duty of care, accuracy standards, the code of ethics, and the legal status of survey records.
Traps in questions
- Scale: RF = map distance / ground distance; a 1:1000 scale means 1 cm = 10 m.
- A plan is large scale; a map is small scale. Do not reverse.
- The north point must be shown; grid north, true north and magnetic north differ.
- Contour interval must be stated on the plan.
- Professional records are legal documents; falsifying them is misconduct.
Worked example / rule of thumb
A line 250 m long is drawn at 1:2500. Map length = 250 / 2500 = 0.10 m = 10 cm. Rule: map length = ground length / scale denominator.
For a graphical scale, draw a line long enough to read the smallest division clearly (about 15 cm), and subdivide the left end into smaller units.