COMPASS TRAVERSING
Compass Introduction and Purpose :
In chain looking over, the region to be overviewed is partitioned into various triangles. This strategy is appropriate
For genuinely level ground covering little regions. However, when the region is enormous, undulating and swarmed with numerous subtleties, triangulation is absurd. In such a region, the strategy for crossing is received.
In crossing, the structure comprises of various associated lines. The lengths are estimated by chain or tape and the bearings recognized by edge estimating instruments. In one of the techniques, the point estimating instruments utilized is the compass. Subsequently, the procedure is known as compass navigating.
NOTE - Consideration of the cross an anticlockwise way is continually useful in running the audit lines.
For genuinely level ground covering little regions. However, when the region is enormous, undulating and swarmed with numerous subtleties, triangulation is absurd. In such a region, the strategy for crossing is received.
In crossing, the structure comprises of various associated lines. The lengths are estimated by chain or tape and the bearings recognized by edge estimating instruments. In one of the techniques, the point estimating instruments utilized is the compass. Subsequently, the procedure is known as compass navigating.
NOTE - Consideration of the cross an anticlockwise way is continually useful in running the audit lines.
DEFINITIONS :
1.True meridian :
The line or plane going through the topographical north post, geological south shaft and any point on the outside of the earth, is known as the 'genuine meridian' or 'topographical merdian'. The genuine meridian at a station is steady. The genuine meridians going through various focuses on the world's surface are not equal, yet join towards the shafts.
Yet, for overviews is little zones, the genuine meridians going through various focuses are expected equal.
The edge between the genuine meridian and a line is known as 'genuine course' of the line. It is otherwise called the 'azimuth'.
2. Magnetic meridian :
At the point when an attractive needle is suspended unreservedly and adjusted legitimately, unaffected by attractive substances, it demonstrates a bearing. This heading is known as the 'attractive meridian'.
The point between the attractive meridian and a line is known as the 'attractive bearing' or just the 'bearing' of the line
3. Arbitrary meridian :
Now and then for the review of little region, an advantageous bearing is expected as a meridian, known as the 'discretionary meridian'. Once in a while the beginning line of a study is taken as the subjective meridian.
The edge between the subjective meridian and a line is known as the 'discretionary course' of the line.
The edge between the subjective meridian and a line is known as the 'discretionary course' of the line.
4. Grid meridian :
Some of the time, for setting up a guide some state organizations expect a few lines parallel to the genuine meridian for a specific zone. These lines are named as 'framework lines' and the focal line the 'network meridian'. The heading of a line as for the matrix meridian is known as the 'framework bearing' of the line.
5. Designation of magnetic bearing :
(i) Whole circle bearing (WCB),
(ii) Quadrantal bearing (QB).
Whole Circle Bearing (WCB) :
The attractive orientation of a line estimated clockwise from the north post towards the line, is known as the 'entire hover bearing', of that line. Such a heading may have any an incentive somewhere in the range of 00 and 3600. The entire hover direction of a line is gotten by kaleidoscopic compass.
Quadrantal Bearing (QB) :
The attractive direction of a line estimated clockwise or counterclockwise from the North Pole or South Pole (whichever is closer the line) towards the East or West, is known as the 'quadrantal heading' of the line. This framework comprises of four quadrant) Quardrantal Bearing (QB s – NE, SE, SW and NW. The estimation of a quadrantal bearing lies somewhere in the range of 00 and 900, yet the quadrants ought to consistently be referenced. Quadrantal direction are gotten by the assessor's compass.
6. Reduced bearing (RB) :
At the point when the entire hover direction of a line is changed over to quadrantal bearing. It is named the 'diminished bearing'. In this way, the diminished bearing is like the quadrantal bearing. Its worth lies somewhere in the range of 00 and 900, yet the quadrants ought to be referenced for legitimate assignment.
7. Fore and back bearing :
The heading of a line estimated toward the advancement of overview is known as the 'front bearing' (FB) of the line.
The heading of a line estimated toward the path inverse to the review is known as the 'back bearing' (BB) of the line
8. Magnetic declination :
The level point between the attractive meridian and genuine meridian is known as 'attractive declination'.
At the point when the north finish of the attractive needle is pointed towards the west side of the genuine meridian, the position is named 'Declination West' ().
At the point when the north finish of the attractive needle is pointed towards the east side of the genuine meridian, the position is named 'Declination East'.
9. Isogonic and agonic lines :
Lines going through purposes of equivalent declination are known as 'isogonic' lines.
Lines going through purposes of zero declination are known as 'agonic' lines.
The Survey of India Department has organized a guide of India in which the isogonic and agonic lines are showed up when in doubt to coordinate the compass review in different bits of the country.
10. Dip of the magnetic needle :
On the off chance that a needle is impeccably adjusted before magnetisation, it doesn't stay in the reasonable position after it is polarized. This is because of the attractive impact of the earth. The needle is observed to be slanted towards the post. This tendency of the needle with the level is known as the 'plunge of the attractive needle'.
It is discovered that the north end of the needle is diverted downwards in the northern half of the globe and that is south end is avoided downwards in the southern side of the equator. The needle is only even at the equator. To adjust the plunge of the needle, a rider (metal or silver loop) is furnished alongside it. The rider is set over the needle at an appropriate position to make it level.
11. Local attraction :
An attractive needle demonstrates the north bearing when unreservedly suspended or rotated. In any case, if the needle draws close to some attractive substances, for example, iron mineral, steel structures, electric links passing on flow; and so forth it is seen as redirected from its actual course, and doesn't show the real north. This upsetting impact of attractive substances is known as 'neighborhood fascination'.
To identify the nearness of neighborhood fascination, the front and back direction of a line ought to be taken. On the off chance that the distinction of the front and back course of the line is actually 1800, at that point there is no neighborhood fascination.
On the off chance that the FB and BB of a line don't vary by 1800, at that point the needle is supposed to be influenced by nearby fascination, if there is no instrumental mistake.
To make up for the impact of nearby fascination, the measure of mistake is discovered and is similarly disseminated between the front and back orientation of the line.
A traverse may be of two types – closed and open.
1. Closed traverse : At the point when a progression of An associated lines shapes a shut circuit, for example at the point when the completing point concurs with the beginning stage harmonizes with the beginning stage of a study, it is known as a 'shut cross'. Here ABCDEA speaks to a shut cross. Shut cross is appropriate for the review of limits of lakes, woodlands bequests, and so on.
2. Open traverse : At the point when a grouping of associated lines reaches out along an overall course and doesn't come back to the beginning stage, it is known as 'open navigate' or 'unclosed cross'. Here ABCDE speaks to an open cross
Open navigate is reasonable for the overview of streets, streams, coast lines, and so forth.
CHECK ON CLOSED TRAVERSE :
(a) The whole of the deliberate inside points ought to be equivalent to (2N – 4) x 900 where N is the quantity of sides of the navigate.
(b) The entirety of the deliberate outside points ought to be equivalent to (2N + 4) x 900.
(c) The arithmetical whole of the redirection points ought to be equivalent to 3600.
Right-hand diversion is viewed as positive and left-hand avoidance negative.
TYPES OF COMPASS :
1. The prismatic compass, and
2. The surveyor’s compass.
1. The prismatic compass : In this compass, the readings are taken with the assistance of a crystal. Coming up next are the fundamental pieces of this compass:
(a) Compass Box The compass box is a round metallic box (the metal ought to be non-attractive) of breadth 8 to 10 cm. A turn with a sharp point is given at the focal point of the container.
(b) Magnetic Needle and Graduated Ring The attractive needle is made of a wide, charged iron bar. The bar is pointed at the two finishes. The attractive needle is joined to a graduated aluminum ring.
The ring is moved on from 00 to 3600 clockwise, and the graduations start from the south finish of the needle. In this way 00 is set apart at the south, 900 at the west, 1800 at north and 2700 at the east. The degrees are again partitioned into half-degrees. The figures are recorded upside. The course of action of the needle and ring contains an agate top turned on the focal rotate point. A rider of metal or silver loop is furnished with the needle to balance its plunge.
(c) Sight Vane and Prism The sight vane and the reflecting crystal are fixed oppositely inverse to the container. The sight vane is pivoted with the metal box and comprises of a horsehair at the inside. The crystal comprises of a locating cut at the top and two little round gaps, one at base of the crystal and the other along the edge of the onlooker's eye.
(d) Dark Glasses Two dull glasses are furnished with the crystal. The red glass is intended for locating radiant articles around evening time and the blue glass for decreasing the strain on the onlooker's eye in splendid sunlight.
(e) Adjustable Mirror A mirror is furnished with the sight vane. The mirror can be brought down or raised, and can likewise be slanted. In the event that any item is excessively low or excessively high as for the view, the mirror can be changed in accordance with watch it through reflection.
(f) Brake Pin A brake pin is given exactly at the base of the sight vane. Whenever squeezed tenderly, it stops the motions of the ring.
(g) Lifting Pin A lifting pin is given just underneath the sight vane. At the point when the sight vane is collapsed, it presses the lifting pin. The lifting pin at that point lifts the attractive needle out of the turn highlight forestall harm to the rotate head.
(h) Glass Cover A glass spread is given on head of the case to shield the aluminum ring from dust.
2. The Surveyor’s compass : The surveyor’s compass is similar to the prismatic compass except for the following points.
(a) There is no crystal on it. Readings are taken with unaided eye.
(b) It comprises of an eye-vane (instead of crystal) with a fine sight cut.
(c) The graduated aluminum ring is connected to the round box. It isn't fixed to the attractive needle.
(d) The attractive needle moves openly over the rotate. The needle shows the perusing on the graduated ring.
(e) The ring is moved on from 00 to 900 out of four quadrants. 00 is set apart at the north and south, and 900 at the east and west. The letters E (east) and W (west) are exchanged from their actual positions. The figures are reviewed the correct way.
(f) No mirror is connected to the item vane.
TEMPORARY ADJUSTMENT OF PRISMATIC COMPASS (FIELD PROCEDURE OF OBSERVING BEARING)
The following procedure should be adopted while measuring the bearing by prismatic compass.
1. Fixing the compass with tripod stand: The tripod stand is put at the necessary station with its legs well separated. At that point the kaleidoscopic compass is held by the left hand and set over the strung head of the stand. After this, the compass box is turned clockwise by the correct hand. Therefore the strung base of the compass box is fixed with the strung head of the stand.
2. Focusing: Normally, the compass is focused by dropping a bit of stone from the base of the compass box. Centring may likewise be finished with the guide of a plumb sway held halfway beneath the compass box.
3. Leveling: Leveling is finished with the assistance of a ball-and-attachment plan gave on head of the tripod stand. This plan is extricated and the container is set so that the graduated ring pivots uninhibitedly without contacting either the base of the case or the glass spread on top.
4.Adjustment of crystal: the crystal is gone here and there till the figures on the graduated ring are seen sharp and clear.
5.Observation of bearing: Subsequent to focusing and leveling the compass box over the station, the extending pole at the necessary station is divided consummately by locating through the cut of the crystal and horsehair at the sight vane.
As of now the graduated ring may pivot quickly. The brake pin is squeezed delicately to stop this revolution. At the point when the ring stops, the case is struck delicately to confirm the horizontality of the ring and the frictional impact on the rotate point. At that point the perusing is taken from the graduated ring through the gap in the crystal. This perusing will be attractive heading of the line.
Compass Traversing Measurment Watch --
QUESTIONS AND ANSWER :-
1 The geographical north pole and
south pole and any point on the surface of the earth is
= true meridian
2 True meridian is also known as
= azimuth
3 WCB full from
= whole circle bearing
4 QB full from
= quadrantal bearing
5 The magnetic bearing of a line
measured clockwise from the north pole it is
= whole circle bearing
6 The magnetic bearing of a line
measured clockwise or anticlockwise from north and south pole it is
= quadrantal bearing
7 RB full from
= reduced bearing
8 The whole circle bearing of a line
converted to quadrantal bearing it is
= reduced bearing
9 forword direction is called
= fore bearing
10 reverseor opposite direction is
called
= back bearing
11 whole circle bearing of a line is
obtained by
= prismatic compass
12 Quadrantal bearing are obtained by
= surveyor’s compass
13 positive sign when fore bearing is
= less than 1800
14 negative sign when
= more than 1800
15 The horizontal angle between the
magnetic meridian and true meridian is
known
= magnetic declination
16 Line passing through points of
equal declination are known
= isogonic line
17 Line passing through points of zero
declination are known
= agonic line
18 Local attraction problem is
= iron ore, steel, electric cables
19 The sum of interior angles of a
closed traverse is
= (2n – 4)* 900
20 The sum of exterior angles of a
closed traverse is
= (2n + 4)* 900
21 The principle of compass surveying
= traversing
22 Close traverse is suitable area
= ponds, forests, etc
23 open traverse is suitable area
= road, rivers, etc
24 The algebraic sum of the deflection
angles should be equl to
= 3600
25 Prismatic compass circular metallic
box diameter
= 8 to 10cm
26 Limits of closing error
= 15’ N
27 In a prismatic compass, the zero is
marked on the
= south end
28 In surveyor compass the ring is
graduated
= 00 to 900
29 The compass box is made of
= brass
30 Open traverse is suitable in the
survey of
= rivers
31 At the equator the dip of the
needle is
= 00
32 At the magnetic pole the dip is
= 900
33 The true meridian passes through
= geographical pole
34 The accuracy of opon traverse is
checked by the
= cut-off line
35 The closing error in a closed
traverse in adjusted by
= bowditch’s rule
36 The lines of force of earth’s
magnetic field are parallel to the earth’s surface
= near the equator
37 The line drawn through the points
of same declination is called
= isogonic line
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