Approximates Methods of Linear Measurements
In reconnaissance survey or to detect chief mistakes committed whereas measuring with better methods, these methods are used. They can give results within 1 %error on smooth roads. These approximate measurements may be by following:
- pacing
- by using passometer
- by using pedometer
- by using odometer
- by using speedometer.
(i) Pacing: surveyor walks along the line to be measured and counts the number of steps in this method. Then the distance measured is equivalent to number of steps × average length of a step. Average length of a step may be found by walking along already known length. A man normally takes a step of length 0.75 m to 0.8 m.
(ii) By Using Passometer: A passometer is a watch-like instrument which can carried vertically in the pocket of shirt or tied to a leg. It measure number of steps taken. So the problem of counting number of steps is eliminated in this approximate method of linear measurement.
(iii) By Using Pedometer: This instrument is similar to passometer but rather then number of steps, it can record the distance. Zero setting and setting of step length is made before walking, in this.
(iv) Odometer: This instrument is attached to the wheel of a cycle or any other vehicle. It records the number of revolutions complete by the wheel. The distance travelled may be found by knowing the circumference of the wheel.
(v) Speedometer: Odometer calibrated to give distance directly is called speedometer. This is only be used for specific vehicle. All of the automobiles are provided with speedometers. Distance can be found by running the vehicle along the line to be measured.