Q16. Radiation, Intersection and Resection are:
📚 Detailed Explanation: The Four Methods of Plane Table Surveying
Radiation, Intersection, and Resection (along with Traversing) are the four standard operational methods used exclusively in plane table surveying. Each serves a different purpose within the same survey.
| Method | Purpose | Station status | Typical use |
|---|---|---|---|
| Radiation | Plot surrounding field details from one station | Known | Detailed mapping of open ground, buildings, roads |
| Intersection | Fix inaccessible or distant points from two known stations | Both known | Hilly areas, far riverbanks, cliffs |
| Resection | Fix the unknown instrument station using known plotted points | Unknown | Setting up at a new convenient station not previously plotted |
| Traversing | Move between successive stations, plotting as you go | Each fixed from previous | Road/river surveys, strip surveys |
Why the Other Options Are Wrong
A — Compass surveying uses a prismatic or surveyor’s compass to measure magnetic bearings between stations. Its methods include fore-bearing, back-bearing, and traversing by bearings — none involve rays drawn graphically on a sheet.
B — Chain surveying is based on linear measurements (chaining) and offsetting, with triangulation as the control. It has no graphical field plotting component.
C — Levelling concerns the measurement of vertical heights and differences in elevation using a level instrument and staff. It has entirely different operational terminology (backsight, foresight, intermediate sight, rise & fall).
Key Concepts for Students
- Four PT methods to memorise: Radiation, Intersection, Resection, Traversing. All four belong exclusively to plane table surveying. No other survey method uses this exact combination of graphical field techniques.
- Each method answers a different question: Radiation answers “what is near me?”; Intersection answers “where is that inaccessible point?”; Resection answers “where am I?”; Traversing answers “how do I move through the area?”
- In practice, methods are combined: A real plane table survey typically uses traversing to move between stations, radiation for detail, and resection/intersection for specific problem spots. They are not used in isolation.