LINEAR MEASUREMENTS AND ANGULAR MEASUREMENTS

Linear Measurements:

•The unit of measurement of distance is metres and centimetres.
•But currently S.I. units are under practice, the unit of linear measurement is metres and millimeters
•However, prior to the introduction of above act in India, the unit of linear measurements are feet, tenth and hundredths of a foot are used.
• Hence a person practicing the surveying now should be able to read the old drawings and change them to the current units.

Instruments used for Linear Measurements

1. By using the following methods the linear measurements are loum approximately

(a) Pacing: The method consists in counting the number of paces (steps) between the two points of a line. The length of the line can then be calculated by knowing the average length of the pace
(b) Passometer: It is an simple instrument like a watch and is carried either in pocket or attached to one leg It automatically counts the paces.
(c) Pedometer: It is a device similar to the passometer, except that, adjusted to the length of the pace of the person carrying it. It directly registers the total distance covered by number of paces
(d) Odometer: It is an instrument for registering the number of revolutions of a wheel. The number of revolutions registered by the odometer multiplied by the circumference of the wheel, gives the distance.
(e) Speedometer: It is an instrument fitted in the automobiles directly register’s the distance.

2. By using the following instruments. Linear measurements are directly find out accurately
(a) Chain
(b) Tape
(c)Offset rod
(d) Level

3. By using the following instruments. Linear measurements are Indirectly determined.
(a) Tacheometer
(b) Geodimeter
(c) Tellurometer
(d) Photographic technique
(e) Total station etc

2. Angular Measurements:

• The unit of angular measurements are radians and degrees, as the case may be
• There are three systems of angular measurements, adopted
•Each system will have its own advantages and disadvantages and adopted suitably depending on the purpose and place.

(a) Sexagesimal System:                                                              1 circumference=360° (degrees of arc) general used
1 degree=60 (minutes of arc) all over the world
1 minute=60″ (seconds of arc) including India

(b) Centesimal System:
1 circumference=400 (grads)It is used
1grad=100° (centigrade)in Europe
1centigrade=100 (centi-centi grads)

(C) Hours Systems:
1circumference=24h (hours) mostly used
1hour=60 (minutes of time)Navigation
1 minute=60 (seconds of time) andAstronomy

Instrument used for Angular Measurements

The following instruments are commonly used for measuring angles in survey work.

1. Prismatic or Surveyor’s compass

2. Pheodolite

3. Box sextant

4. Abney level

5 Indian pattern clinometer.

6 Total station etc.