The various methods of measuring the distances directly are as follows:
2. Measurement with passometer
3. Measurement with pedometer
4. Measurement by odometer and speedometer
1) Pacing :
Measurements of distances by pacing is chiefly confined to the preliminary
surveys and explorations where a surveyor is called upon to make a rough survey as quickly as possible.
It may also be used to roughly check the distances measured by other means.
The method consists in counting the number of paces between the two points of a line.
The length of the line can then be computed by knowing the average length of the pace.
The length of the pace varies with the individual, and also with the nature of the ground, the slope of the country and the speed of pacing.
A length of pace more nearly that of one’s natural step is preferable.
The length of one’s natural step may be determined by walking on fairly level ground over various lines of known lengths.
One can soon learn to pace distances along level, unobstructed ground with a degree of accuracy equivalent approximately to 1 in 100.
However, pacing over rough ground or on slopes may be difficult.
2) Passometer :
Passometer is an instrument shaped like a watch and is carried in pocket or attached to one leg.
The mechanism of the instrument is operated by motion of the body and it automatically registers the number of paces, thus avoiding the monotony and strain of counting the paces, by the surveyor.
The number of paces registered by the passometer can then be multiplied by the average length of the pace to get the distance.
3) Pedometer :
Pedometer is a device similar to the passometer except that, adjusted to the length of the pace of the person carrying it, it registers the total distance covered by any number of paces.
4) Odometer and Speedometer :
The odometer is an instrument for registering the number of revolutions of a wheel.
The well-known speedometer works on this principle.
The odometer is fitted to a wheel which is rolled along the line whose length is required.
The number of revolutions registered by the odometer can then be multiplied by the circumference of the wheel to get the distance.
Since the instrument registers the length of the surface actually passed over, its readings obtained on undulating ground are inaccurate.
If the route is smooth, the speedometer of an automobile can be used to measure the distance approximately.
5) Chaining :
Chaining is a term which is used to denote measuring distance either with the help of a chain or a tape and is the most accurate method of making direct measurements.
For work of ordinary precision, a chain can be used, but for higher precision survey can a tape or special bar can be used.
The distances determined by chaining form the basis of all surveying.
No matter how accurately angles may be measured, the be no more precise than the chaining.