This article throws light upon the four main direct methods that are available for measuring distance. The direct methods are: 1. Pacing 2. Instrumental Method 3. Judging Distance and Time Measurements 4. Chaining.
Direct Method # 1. Pacing:
The method consists in walking over a line and counting the number of paces. The average pace length may be taken as 80 cm. However, the surveyor should standardise his pace length by practice. The distance may then be obtained by multiplying the number of paces with the average length of the pace.
An experienced person can attain results within an accuracy of 1 in 100. The method is generally useful where approximate results are required such as for reconnaissance survey, locating details in small scale mapping etc.
The method, though rapid, is tiresome for long distances and also great difficulty is experienced in counting the number of paces. To overcome this difficulty, an instrument resembling a pocket watch in size and appearance and known as passometer may be used, which automatically records the number of paces while pacing a given line.
Direct Method # 2. Instrumental Method:
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Some instruments like Speedometer of an automobile, Pedometer etc. may also be employed to find the distance approximately. Speedometer gives better results than pacing provided the route is smooth as along a highway.
Direct Method # 3. Judging Distance and Time Measurements:
For very approximate results such as in reconnaissance survey, the distances may be determined by judgement only. The distances are also roughly determined by knowing the average time taken per km by a person at walk or a horse at trot and the total time taken to cover that distance.
Direct Method # 4. Chaining:
The operation of measuring distance with the help of a chain or a tape is called chaining. It is the most accurate of all the methods of measuring distance and is commonly used. Ordinarily a chain is used for measuring the distance but where great accuracy is required, a steel tape is invariably used.