Angular measurement a part of surveying

1. ELEMENTS OF CIVIL ENGINEERING
SAGAR DOBARIYA
Asst. professor
Civil Engineering Department
Om Engineering College, Junagadh.

2. ANGULAR MEASUREMENT

4. 1. Cylindrical metal box :
 Cylindrical metal box is having diameter of 8 to 12 cm.
 It protects the compass and forms entire casing or body of
the compass.
 It protects compass from dust, rain etc.
2. pivot :
 Pivot is provided at the center of the compass and supports
freely suspended magnetic needle over it.
3. Lifting level :
 Lifting pin is provided just below the sight vane.
 When the sight vane is folded it presses the lifting pin.
 The lifting pin with the help of lifts the magnetic needle out
of pivot point to prevent damage to the pivot

5. 4. Magnetic needle :
 Magnetic needle is a heart of the instruments.
 This needle measured angle of a line from magnetic meridian as the
needle always remains pointed toward north and south pole at two
ends of needle
5. Graduated ring :
 This is an aluminum graduated ring marked with 0* to 360* to
measure all possible bearing of lines and attached with the magnetic
needle.
 The ring is graduated to half a degree.
6. prism :
 Prism is used read graduation on ring and to take exact reading by
compass.
 It is placed exactly opposite to object vane.
 The prism hole is protected by prism cap to protect it from dust and
moisture.

6. 7. Object vane :
 Object vane is diametrically opposite to the prism and eye
vane.
 The object vane is caring a horse hair or black thin wire
to sight object in line with eye sight.
8. Eye vane :
 Eye vane is a fine slit provided with the eye hole at
bottom to bisect the object from the slit and to take
reading simultaneously from eye hole.
9. Glass cover :
 It covers the instrument box from the top such that needle
and graduated ring is seen from the top.

7. 10. Sun glasses :
 These are used when some luminous objects are to be bisected.
 These are placed in front of the eye slit and in bunch of three or
four shades of different colors to give sharp picture of the object
only.
11. Reflecting mirror :
 It is used to get image of an object located above or below the
instrument level while bisection.
 It is placed on the object vane.
12. Spring brake or brake pin :
 To damp the oscillation of the needle before taking a reading and
to bring it to rest quickly.
 The light spring brake attached to the inside of the box is brought
in contact with the edge of the ring by gently pressing inward the
brake pin.

8. No. Prismatic compass Surveyor’s compass
1 The graduated ring is attached
to the magnetic needle
The graduated ring and needle are
free to move independently with
respect to each other
2 Graduated ring remain
stationary while box with
prism and object vane rotates
as the ring attached with
needle is not attached with the
box
Graduated ring rotates with
rotation of box, eye vane and
object vane as the ring is attached
with the box of the compass and
only needle remains stationary
3 Prism is provided to take
reading and thus the
graduated ring is marked with
the figures of mirror image.
The graduated ring is graduated
with ejected figure and no prism
is provide to take reading.

9. 4 Graduation are marked 0* and
360* in clockwise direction
Graduations are marked 0* to 90*
in each quadrant
5 0* is marked at south, 180* at
north, 90* at west and 270* at
east marked
In this compass east and west is
inter-changed
6 Tripod may or may not be
provided
The instrument cannot be used
without a tripod
7 It measured or given W.C.B. of
a line
It measured or gives Q.B. of a
line
8

10.  Bearing of a line always measured clockwise with
respect to some reference line or direction.
 This fixed reference and line is known as meridian.
 Tree type of bearing
1. Magnetic meridian :
 The direction shown by a freely suspended needle
which is magnetized and balanced properly without
influenced by any other factors is known as magnetic
meridian.
 Magnetic bearing of a line is the horizontal angle
formed by the line with the magnetic meridian

11. 2. True meridian :
 True meridian is the line which
Passes through the true north and
South.
 True baring is the horizontal
which the line makes with the true meridian is known as the
true bearing.
3.Arbitrary meridian :
 In case of small work or in place where true meridian or
magnetic meridian cannot be determined then any direction
of a prominent object is taken as a reference direction
 The horizontal angle made by a line with the arbitrary
meridian is called arbitrary bearing

12.  Bearing of a line always measured clockwise with
respect to some reference line or direction.
 four type of bearing
1. Magnetic bearing :
 Magnetic bearing of a line is the horizontal angle which
the line makes with the magnetic north.

13. 2. True bearing :
 True baring is the horizontal which the line makes with
the true meridian is known as the true bearing.
 True bearing is measured from the true north in the
clockwise direction
3.Arbitrary meridian :
 The horizontal angle made by a line with the arbitrary
meridian is called arbitrary bearing
4.Grid meridian :
 The grid bearing of a line is the horizontal angle which
the line make with the grid meridian

14.  The bearing of a line measured with
Respect to magnetic bearing and its value
Varies between 0* to 360*
 The quadrant is start from north and
Progress in a clockwise direction as the
First quadrant 0* to 90* in clock wise
Direction, 2nd 90* to 180*,
3rd 180* to 270* and 4th 270* to 360*
 The prismatic compass measures the bearing of line in
the whole circle system.

15.  In this system the bearing of
Survey lines are measured with
Respect to north line or south line
Which ever is the nearest to the
Given survey line and either in clock
wise direction or in anticlockwise
Direction.
 The 1st quadrant is called NE, 2nd quadrant as SE, 3rd
quadrant as SW and 4th quadrant as NW.

16.  The bearing of lines which fall in 1st and 4th quadrant
are measured with respect to north line as north is
nearer than south line and bearing of lines fall in 2nd
and 3rd quadrant are measured from south line as south
is the nearer line.
 The surveyor’s compass measures the bearing of lines
in the quadrant system.

17.  When the whole circle bearing of a line is converted
into quadrant bearing. It is called as reduced bearing
 The reduced bearing is similar to the quadrant bearing
 It values lies between 0* to 90* but the quadrant should
be mentioned for proper designation.
 For converted of WCB to RB.
W.C.B. Quadrant conversion Direction
0* to 90* 1st RB = WCB N - E
90* to 180* 2nd RB = 180*- WCB S - E
180* to 270* 3rd RB = WCB – 180* S-W
270* to 360* 4th RB = 360* -WCB N -W

18.  The horizontal angle between true north and magnetic
north at a place at the time of observation is called
magnetic declination.
 The horizontal angle between the magnetic meridian
and true meridian is known as magnetic declination
 when the north end of the magnetic needle is pointed
towards the west side of the true meridian the position
as declination west
 When the north end of the magnetic needle is pointed
towards the east side of the true meridian the position
as declination east

19.  Lines passing through points of equal declination are know
as isogonics lines
 Lines passing through points of zero declination is known
as agonic lines
 There are four types of variations of declination
1. Secular variation 2. Annual variation
3. Diurnal variation 4. Irregular variation