Q11. What is the purpose of conducting the resection method in plane table surveying?
Correct Answer: A. To determine the location of the instrument
📚 Detailed Explanation: Purpose of the Resection Method
Resection is one of the four standard methods of plane table surveying (alongside radiation, intersection, and traversing). Each method serves a distinct purpose, and understanding what each achieves is a common exam focus.
Resection purpose: To establish the position of the occupied instrument station on the drawing sheet when that station’s location is not already known. In other words, it answers the question: “Where is the plane table right now?”
Rays are drawn from the plotted positions of three visible, known control points toward the unknown instrument station. After orientation, the intersection of these rays fixes the station’s position on the sheet.
Why the Other Options Are Wrong
| Option | What it actually describes |
|---|---|
| B — To plot the details | Plotting field details (roads, rivers, buildings, contours) is done using the radiation method: from a known station, rays are drawn toward detail points and distances scaled onto the rays. |
| C — To survey hilly region | Hilly or rugged terrain where direct distance measurement is difficult is best handled by the intersection method, where an inaccessible feature is located from two known stations by the intersection of two sighting rays. |
| D — To survey plain region | Surveying a plain region is not the defining purpose of any single plane table method. Radiation and traversing are both used in flat open ground. Option D is a distractor with no specific method association. |
Four Methods and Their Purposes
| Method | Primary purpose | Station status |
|---|---|---|
| Radiation | Plotting surrounding field details from one station | Known |
| Intersection | Locating inaccessible points using two instrument stations | Both known |
| Resection | Determining the instrument station’s own position | Unknown (being fixed) |
| Traversing | Running a connected series of stations through the area | Each fixed from the previous |
Key Concepts for Students
- Resection = fixing the instrument station: Always remember: resection answers “where am I?” It is used when the surveyor sets up at a new station whose position on the sheet has not yet been established. The two sub-problems (two-point and three-point problems) are both resection variants.
- Contrast with intersection: Intersection also uses rays from multiple known points, but the goal is different — it fixes the position of an external target, not the instrument. In resection, the instrument is at the unknown location; in intersection, the target is at the unknown location.
- Practical use case: Resection is valuable in large-scale surveys where the surveyor needs to set up at a convenient ground point (e.g., a hilltop or road junction) that has not been previously plotted, and quickly establishes its position using three visible known trigonometric stations without moving to any of those stations.