The method of reciprocal ranging can be used in which of the following cases?
📝 Detailed Explanation: Understanding Obstacles in Chaining
In surveying, obstacles can interfere with the two primary operations of chaining: the physical measurement of distance (chaining) and the alignment of points in a straight line (ranging). Different obstacles require different methods to overcome them.
What is Reciprocal Ranging? (Corrects Obstacles to Ranging)
Reciprocal ranging is a special method used specifically when the two endpoints of a survey line are not intervisible due to a high point of ground, like a hill or a ridge, between them. In this scenario:
- Ranging is obstructed: You cannot see from station A to station B to visually align intermediate points.
- Chaining is NOT obstructed: You can physically walk over the hill and lay the chain along the ground between the two points.
The method involves placing surveyors on the high ground who can see both endpoints. Through a series of signals, they guide intermediate ranging rods into the correct straight line. Therefore, reciprocal ranging is the precise solution for an obstacle to ranging but not chaining, making option (d) the most accurate answer.
Analysis of Obstacle Types
Let's classify the common obstacles encountered in the field:
| Type of Obstacle | Example | Chaining | Ranging | Standard Method Used |
|---|---|---|---|---|
| Obstacle to Ranging only | Rising ground, hill, intervening trees | Possible (Free) | Obstructed | Reciprocal Ranging |
| Obstacle to Chaining only | River, pond, hedge | Obstructed | Possible (Free) | Geometric methods to calculate distance |
| Obstacle to Both | Building | Obstructed | Obstructed | Special methods (e.g., running parallel lines, geometry) |
Based on this classification:
- (a) Obstacle to chaining but not ranging: This describes a river or pond. While ranging is possible (you can see across), the standard solution is not reciprocal ranging, but rather using geometric principles to find the width.
- (b) Obstruction by a building: This is an obstacle to both chaining and ranging.
- (c) Obstruction by a river: This is a classic obstacle to chaining, but ranging is typically possible. As noted, this can cause confusion, but the specific technique of reciprocal ranging is not the standard method here.
Therefore, the only case that directly and correctly calls for the method of reciprocal ranging is when there is an obstacle to ranging but not to chaining.