Resection in Plane Table Surveying Explained

The process described in the question is a fundamental technique in plane table surveying used to determine the exact location of the plane table station (where the surveyor is standing) on the map.

What is Resection?

Resection involves orienting the plane table and plotting the instrument's station position using bearings taken from the station to two or more known points (points whose locations are already plotted on the map or are known reference points). The surveyor sets up the plane table at an unknown location, sights known points, and uses these observations to pinpoint their own location on the plan.

How Resection Works:

• The plane table is oriented using a known direction (e.g., magnetic north or a previously plotted line).
• The alidade is used to sight known objects (e.g., triangulation stations, prominent landmarks).
• Lines are drawn on the drawing sheet along the direction of sight towards these known points.
• The intersection of these lines (or rays) drawn from the station to the known points indicates the actual position of the plane table station on the map. This is often done using the three-point problem method if three known points are sighted.

Comparing Resection with Other Methods:

It's helpful to understand why other options are not the correct term:

• Radiation: This method involves setting up the plane table at a known station and sighting various points to be plotted. Distances are measured (e.g., using a chain or EDM) and plotted directly from the station, radiating outwards. It's used to plot points relative to a known station, not to find the station itself.
• Intersection: In this method, the plane table is set up at two known points. The unknown point (station) is sighted from both known locations. Rays are drawn towards the unknown station from each known point. The intersection of these rays on the map locates the unknown station. This is different from resection, where the surveyor is *at* the unknown station.
• Traversing: Traversing involves establishing a series of connected points (stations) by measuring distances and angles between them. The plane table is moved from station to station, creating a framework or traverse line. While resection might be used to orient the table during traversing, traversing itself is the process of establishing the control line.

Therefore, the specific process of determining the station's plotted position by taking sights towards known points is called resection.