Short Answer:
The collimation method in leveling is a technique used to determine the elevation of different points by referring all measurements to a single horizontal line of sight. It involves taking staff readings at multiple points and calculating their heights relative to a known reference point. This method is faster and easier for long-distance leveling compared to other techniques. It is commonly used in surveying for road construction, land grading, and infrastructure projects.
Detailed Explanation:
The collimation method (also called the height of instrument (HI) method) is one of the two main techniques used in leveling to determine the elevation of different points. It is preferred when surveying large areas because it reduces calculation errors and simplifies the process.
Principle of the Collimation Method:
- A leveling instrument is set up at a convenient point, and the height of the instrument (HI) is calculated by adding the staff reading at a known benchmark (BM) to its reduced level (RL).
- All further height measurements are taken by subtracting the staff readings from the HI.
- This method ensures that all readings are related to a single horizontal line of sight, making calculations simpler and faster than the rise and fall method.
Steps to Perform the Collimation Method:
- Setup the Leveling Instrument:
- Place the instrument at a stable location and adjust it to achieve a clear horizontal line of sight.
- Determine the Height of the Instrument (HI):
- Take a back sight (BS) reading on a known benchmark (BM).
- Add the BS reading to the BM’s reduced level (RL) to get the HI:
HI = RL of BM + BS
- Take Fore Sight (FS) and Intermediate Sight (IS) Readings:
- Measure staff readings at different points.
- Calculate the reduced level (RL) of each point using:
RL = HI – Staff Reading
- Repeat for Other Points:
- If the instrument is moved, repeat the process using the new benchmark.
Advantages of the Collimation Method:
- Faster and simpler calculations compared to the rise and fall method.
- Less chance of mistakes since all points are related to a single reference line.
- Useful for long-distance surveys, such as roads, railways, and pipelines.
Disadvantages:
- Less accurate for detecting errors in readings compared to the rise and fall method.
- Requires a clear line of sight, which may be difficult in uneven terrains.
Conclusion:
The collimation method is a reliable and efficient technique for leveling in surveying. It simplifies height calculations by using a common height of instrument (HI) for all points. This method is widely used in construction, land surveying, and road development due to its ease of use and quick calculations.