Prismatic compass, surveyor's compass, bearing systems and conversions, local attraction, magnetic declination, dip traversing, adjustment of errors

1. Module 2: Compass
Surveying
Prepared By-
Prof. Basweshwar S. J.

2. Compass surveying is the branch of surveying in which the position
of an object is located using angular measurements determined by a
compass and linear measurements using a chain or tape.
o If the surveying area is large, chain surveying is not adopted for
surveying rather compass surveying is employed.
o If the plot for surveying has numerous obstacles and undulations
which prevents chaining.
o If there is a time limit for surveying, compass surveying is
usually adopted
Prepared By-
Prof. Basweshwar S. J.

3. Prepared By-
Prof. Basweshwar S. J.

4. Prepared By-
Prof. Basweshwar S. J.

5. Major parts of a Prismatic Compass
are:
•Magnetic needle
•Graduated ring
•Adjustable mirror
•Sliding arrangement for mirror
•Object vane
•Eye vane
•Metal box
•Glass cover
•Horse hair
Prepared By-
Prof. Basweshwar S. J.

6. Bearing Systems And Conversions
Prepared By-
Prof. Basweshwar S. J.

7. Bearing Systems And Conversions
Prepared By-
Prof. Basweshwar S. J.

8. Bearing Systems And Conversions
• The word azimuth came from a word
of Arabic origins, ‘as-sumut’,
• It means – ‘the way or direction’.
• When one refers to azimuth, it is a
determination of a direction with the
use of a compass.
• The reference is North, which is 0 or
360 degrees.
• In land surveying, a bearing is the
clockwise or counterclockwise angle
between north or south and a
direction.
Prepared By-
Prof. Basweshwar S. J.

9. Prepared By-
Prof. Basweshwar S. J.

10. Prepared By-
Prof. Basweshwar S. J.

11. Prepared By-
Prof. Basweshwar S. J.

12. LOCAL ATTRACTION
• While compass surveying, the magnetic
needle is sometimes disturbed from its
normal position under the influence of
external attractive forces. Such a
disturbing influence is called as local
attraction.
• The external forces are produced by
sources of local attraction which may be
current carrying wire (magnetic
materials) or metal objects.
• It mostly causes errors in observations
while surveying and thus suitable
methods are employed to neglect these
errors. Prepared By-
Prof. Basweshwar S. J.

13. MAGNETIC DECLINATION
• Magnetic declination, or
magnetic variation, is the angle
on the horizontal plane between
magnetic north and true north
(the direction along a meridian
towards the geographic North
Pole).
• This angle varies depending on
position on the Earth's surface
and changes over time.
Prepared By-
Prof. Basweshwar S. J.

14. MAGNETIC DIP
Magnetic dip, dip angle, or magnetic
inclination is the angle made with the
horizontal by the Earth's magnetic field
lines.
This angle varies at different points on
the Earth's surface.
Positive values of inclination indicate
that the magnetic field of the Earth is
pointing downward, into the Earth, at
the point of measurement, and negative
values indicate that it is pointing
upward.
Prepared By-
Prof. Basweshwar S. J.

15. TRAVERSING
Prepared By-
Prof. Basweshwar S. J.

16. TRAVERSING
Prepared By-
Prof. Basweshwar S. J.