Q1. In regard to the resection method of plane table survey, the term ‘resector’ refers to the:
📚 Detailed Explanation: The Resection Method & the Meaning of ‘Resector’
Resection is one of the four core methods of plane table surveying. Its purpose is to establish the position of an unknown instrument station on the drawing sheet by drawing lines of sight toward control points whose positions have already been plotted. The key term, resector, precisely defines those sighting rays.
Fig 1: In resection, the plane table sits at unknown station p. Dashed rays (resectors) are drawn from p toward already-plotted known points a, b, c to fix p on the sheet.
Why Option B is Correct
The plane table is set up over a new ground station p whose position on the sheet is not yet known. The surveyor sights three visible, pre-plotted reference stations a, b, c and draws rays from the (currently unknown) instrument position toward those known plotted points. These lines are the resectors. After applying Lehmann’s rules or another orientation technique, the point where the resectors converge is the fixed position of p on the sheet.
Why the Other Options Are Wrong
| Option | Direction described | What method this actually describes |
|---|---|---|
| A | Known station → un-plotted points | Radiation: from a known, plotted station you draw rays to unknown field features to locate them. |
| C | Known station → known points | Back-sighting between two already-plotted stations for orientation. No unknown position is being determined. |
| D | Unknown station → unknown points | Both ends are unplotted, so no reference exists to fix either. This does not correspond to any valid survey method. |
Resection vs Intersection vs Radiation: Key Differences
| Method | Instrument station | Target | What is fixed |
|---|---|---|---|
| Resection | Unknown (to be located) | Known, plotted points | Position of instrument station |
| Intersection | Known, plotted | Unknown field feature | Position of target feature |
| Radiation | Known, plotted | Multiple unknown details | Positions of many field features |
Key Concepts for Students
- Resectors go from unknown to known: The prefix “re-” means “back.” Rays go from the new unlocated station back toward reference points already on the map. This is the opposite of the radiation method where rays go outward from a known station to unknown features.
- Resection solves the “where am I?” problem: You stand at a new station, you can see known landmarks, and you need to plot your position. Resectors from three known points converge to fix your location. Using only two gives a fix but no check; three rays provide both a fix and an error triangle for quality control.
- Common exam trap — direction of rays: Questions often swap “known station” and “un-plotted station” deliberately. Always ask: which end is the instrument? In resection, the instrument is at the unknown end, so rays go from unknown to known — Option B.