types of meridians

1. Types of Compass, Types of Meridians,& Types of
Bearing.
Element Of Civil Engineering
Prepared by :-
Kundariya Ankit
Patel Avi
Patel Dharmik
Prof. Saurabh Shah
Guided by :-

2. • A Compass is an instrument containing a magnetized pointer which
shows the direction of magnetic north and bearings from it.
What is Compass?
Types of Compass:
• Prismatic Compass
• Surveyor’s Compass
• A Prismatic compass is a navigation and
surveying instrument which is extensively used
for determining course, waypoints and
direction, and for calculating bearings of survey
lines and included angles between them.
• A Surveyor's compass, is an instrument used
in surveying to measure horizontal angles. It
was superseded by the theodolite in the early
19th century.

3. Prismatic Compass Surveyors' Compass

4. Prismatic Compass Surveyor’s Compass
The Graduated ring attached to the
magnetic needle.
The Graduated ring and needle are free to
move independently wrt each other
Graduated ring remains stationary while
box is prism and object vane rotates as
the ring attach with needle is not attach
with the box
Graduated ring rotates with rotation of box
,eye vane & object vane as the ring is attach
with the box of the compass & only needle
remains stationary
Prism is provided to take reading The graduated ring is graduated with ejected
figures and no prism is provided to take the
reading
Graduation are marked 0 to 360 in
clockwise direction
Graduations are marked 0 to 90 in each
quadrant
Tripoid may or may not be provided. The instrument cannot be used without tripoid
It measures or gives WCB of a line It measures or gives Q.B. of a line.

5. Compass Surveying
• Chain Surveying can be used when the
Area to be surveyed is comparatively
small and is fairly flat.
• But when the area is large, undulated
and crowded with many details,
triangulation(which is the principle of
chain survey) is not possible. In such an
area, the method of traversing is
adopted.

6. Principle of Compass Surveying:
• The Principle of compass survey is Traversing; which involves a series of
connected lines the magnetic bearing of the lines are measured by
prismatic compass and the distance (lengths) are measured by chain.
• Such survey does not require the formulation of a network of triangle.
• Compass surveying is recommended when the area is large, undulating
and crowded with many details.
• Compass surveying is not recommended for areas where local
attraction is suspected due to the presence of magnetic substances like
steel structures, iron ore deposits, electric cables conveying currents.

7. • In traversing , the frame work consist of connected lines.
• The length are measured by a chain or a tape and the
direction measured by angle measuring instruments.
• Hence in compass surveying direction of survey lines
are determined with a compass and the length of the
lines are measured with a tape or a chain. This process is
known as compass traversing.
Traversing

8. Types of Bearing:-
The bearing of a line is the horizontal angle which it makes
with a reference line(meridian).
there are four type of bearings :-
1) True Bearing: The true bearing of a line is the horizontal
angle between the true meridian and the survey line. The
true bearing is measured from the true north in the
clockwise direction.
2) Magnetic Bearing: the magnetic bearing of a line is the
horizontal angle which the line makes with the magnetic north.
3) Grid Bearing: The grid bearing of a line is the horizontal
angle which the line makes with the grid meridian.
4) Arbitrary Bearing: The arbitrary baring of a line is the
horizontal angle which the line makes with the arbitrary
meridian.

9. BEARINGS
TRUE
MERIDIAN
MAGNETIC
MERIDIAN
TRUE BEARING
MAGNETIC
BEARING
A
B
MN
TN

10. The bearing are designated in the following two system:-
1) Whole Circle Bearing System.(W.C.B)
2) Quadrantal Bearing System.(Q.B)
Measurement of Bearings :

11. • The bearing of a line measured with respect to magnetic meridian
in clockwise direction is called magnetic bearing and its value
varies between 0ᴼ to 360ᴼ.
• The quadrant start from north an progress in a clockwise direction
as the first quadrant is 0ᴼ to 90ᴼ in clockwise direction , 2nd 90ᴼ to
180ᴼ , 3rd 180ᴼ to 270ᴼ, and up to 360ᴼ is 4th one.
Whole Circle Bearing System.(W.C.B)
• In this system, the bearing of survey lines are
measured wrt to north line or south line which ever
is the nearest to the given survey line and either in
clockwise direction or in anti clockwise direction
Quadrantal bearing system(Q.B.)

12. • When the whole circle bearing is converted into
Quadrantal bearing , it is termed as “REDUCED BEARING”.
Thus , the reduced bearing is similar to the Quadrantal
bearing.
• Its values lies between 0ᴼ to 90ᴼ, but the quadrant should
be mentioned for proper designation.
Reduced bearing (R.B)
W.C.B OF ANY
LINE
QUADRANT IN
WHICH IT LIES
RULES FOR
CONVERSION
QUADRANT
0 TO 90 I RB=WCB N-E
90 TO 180 II RB=180-WCB S-E
180 TO 270 III RB =WCB-180ᴼ S-W
270 TO 360 IV RB=360ᴼ - WCB N-W

13. Fore bearing and Back bearing
The bearing of a line measured in the forward direction of the survey
lines is called the ‘fore bearing’(F.B.) of that line.
The bearing of a line measured in direction backward to the direction of
the progress of survey is called the ‘back bearing’(B.B.) of the line.

14. Types of Meridians:
•Magnetic meridian :- The direction shown by a freely
suspended needle which is magnetised and balanced
properly without influenced by other factors is known as
magnetic meridian
•True meridian :- True meridian is the line which passage
through the true north and south. The true meridian at any
point can be determinate by either observing the bearing of
the sun at 12 noon or by sun’s shadow.
•Arbitrary meridian :- In case of small work or in places were
true meridian or magnetic meridian cannot be determined,
then any direction of prominent object is taken as a reference
direction called as arbitrary meridian.

15. Example of WCB into Reduced
Bearings:-
• Convert the following WCB into RB

18. • S 43 °15’ E

19. Example :- 1

20. Note :- If FB > 180 then subtraction is required
And if FB<180 then addition is required

21. Example 2 :-
The following bearings were taken of a closed traverse ABCD.
Line FB BB
AB 45°00’ 225°00’
BC 123°30’ 303°00’
CD 181°00’ 1°00’
DA 289°00’ 109°00’
Calculate the interior angels of the traverse.

22. Station Line FB Line BB Diff of FB &
BB
Exterior
Angle
Interior
Angle
A AB 45°00’ DA 109°00’ 64°00’ 64°00’
B BC 123°3’ AB 225°00’ 101°00’ 101°30’
C CD 181°0’ BC 303°30’ 122°30’ 122°30’
D DA 289°0’ CD 1°00’ 288° 288° 72°00’
Interior angle A = BB of DA – FB of AB
Interior angle B = BB of AB – FB of BC
Interior angle C = BB of BC – FB of CD
Exterior angle D = FB of DA – BB of CD
So the Interior angle D = 360° – Interior angle D
Sum of angles = 64°+101°30’+122°30’+72°
= 360 °
Check = (2N – 4 ) * 90°
= (2*4 – 4 )*90 °
= 360 °

23. Example 3 :- The Details of observed bearings are mentioned below.
Find out the included angles and correct the angles if needed to be
corrected.
LINE FB BB
AB 20°30’ 200°00’
BC 110°00’ 290°30’
CD 195°00’ 15°00’
DA 286°30’ 106°00’

24. Station Line FB Lin
e
BB Diff. of FB
& BB
Exterior
Angle
Interior
Angle
A AB 20°30’ DA 106°0’ 85°30’ 85°30’
B BC 110°00’ AB 200°00’ 90°00’ 90°00’
C CD 195°00’ BC 290°30’ 95°30’ 95°30’
D DA 286°30’ CD 15°00’ 271°30’ 271°30’ 88°30’
Sum = 359°30’
Interior angle A = BB of DA – FB of AB
Interior angle B = BB of AB – FB of BC
Interior angle C = BB of BC – FB of CD
Exterior angle D = FB of DA – BB of CD
So the Interior angle D = 360° – Interior angle D
Sum of angles = 85°30’+90°00’+95°30’+88°30’= 359°30’
Check = (2N – 4 ) * 90°
= (2*4 – 4 )*90 °
= 360 °
Total Error = 359°30’ – 360° = – 30°∴

25. Total Correction = +30’∴
∴ Correction per angle = + 30’/4 = + 7’30”
Corrected value :-
Angle Calculated value Correction Corrected included
Angle
A 85°30’ + 7’30” 85°37’30”
B 90°00’ + 7’30” 90°07’30”
C 95°30’ + 7’30” 95°37’30”
D 88°30’ + 7’30” 88°37’30”
Sum 359°30’ + 30’00” 360°00’00”