Subtense Bar for Measurement of Horizontal Distances in Undulated Areas

Subtense bar is an instrument that is commonly used in surveying to measure horizontal distances in undulated areas. It is a type of tacheometer, which is an instrument used for measuring horizontal and vertical distances.

Principle of Operation:

The subtense bar works on the principle of subtense. The subtense is the apparent width of an object when viewed from a distance. The subtense bar consists of two telescopic tubes, which are connected to each other by a hinge. The hinge allows the tubes to be set at a fixed angle to each other.

Measurement Procedure:

The measurement procedure involves the following steps:

1. The subtense bar is set up on a tripod at a known point.

2. The operator looks through one of the telescopic tubes and aligns it with a target at the other end of the distance to be measured.

3. The operator then looks through the other telescopic tube and aligns it with a second target at the other end of the distance to be measured.

4. The operator then measures the distance between the two targets using a tape measure or other distance measuring device.

Advantages:

The subtense bar has several advantages over other distance measuring instruments, including:

1. It is relatively easy to use and requires no specialized training.

2. It can be used in areas with undulating terrain where other instruments may not be suitable.

3. It is relatively inexpensive compared to other distance measuring instruments.

Disadvantages:

The subtense bar also has some disadvantages, including:

1. It is not as accurate as other distance measuring instruments, such as the total station.

2. It requires the operator to have a clear line of sight between the two targets, which may not always be possible in areas with dense vegetation or other obstacles.

Conclusion:

In summary, the subtense bar is a useful instrument for measuring horizontal distances in undulated areas. While it may not be as accurate as other instruments, it is relatively easy to use and can be used in areas where other instruments may not be suitable.