Obstacles in Surveying: Chaining vs. Vision
(A) River
(B) Hill
(C) Missing ground
(D) All of the above
Explanation
In surveying, chaining refers to the process of measuring distances on the ground using a chain or tape. An obstacle that obstructs chaining prevents the physical placement of the chain, while an obstacle that obstructs vision blocks the line of sight between two points. A river obstructs chaining because it is difficult to stretch a chain or tape across water, but it does not typically obstruct vision, as you can see across the river to the other side.
Comparison of Obstacles
The following table compares the effects of different obstacles on chaining and vision in surveying:
| Obstacle | Effect on Chaining | Effect on Vision |
|---|---|---|
| River | Obstructs (cannot easily stretch chain across water) | Does not obstruct (clear line of sight across water) |
| Hill | Obstructs (difficult to chain over steep or uneven terrain) | Obstructs (blocks line of sight depending on height and position) |
| Missing Ground | Obstructs (gaps or voids prevent chaining) | Obstructs (gaps may block line of sight) |
Key Concepts
- Chaining: The process of measuring distances using a chain, tape, or other physical tools. Obstacles like rivers, hills, or missing ground (e.g., ravines) make direct measurement challenging.
- Vision: Refers to the line of sight required for sighting instruments (e.g., theodolite, level). Obstacles like hills or missing ground can block vision, while rivers typically do not.
- Surveying Techniques: To overcome chaining obstacles, surveyors may use methods like triangulation, offsetting, or electronic distance measurement (EDM).
Summary Table
| Obstacle | Obstructs Chaining | Obstructs Vision |
|---|---|---|
| River | Yes | No |
| Hill | Yes | Yes |
| Missing Ground | Yes | Yes |
Key Notes
- A river is a classic example of an obstacle that obstructs chaining but not vision, making it the correct answer.
- Hills and missing ground (e.g., ravines or cliffs) typically obstruct both chaining and vision, depending on their size and position.
- Surveyors must adapt techniques (e.g., using ranging rods, EDM, or triangulation) to measure distances across obstacles like rivers.
- Understanding the impact of obstacles is crucial for accurate surveying in civil engineering and land measurement.
Note: Proper identification of obstacles and their effects on chaining and vision is essential for effective surveying and ensuring accurate measurements in the field.
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