Plane Table Surveying - Basics,Setup & Methods,Examples, etc

                           Plane Table Surveying

What is Plane Table Surveying?

The plane table looking over is the quick technique for studying. In this kind of reviewing plotting of the arrangement and field perceptions should be possible all the while. If there should be an occurrence of plane table reviewing Geometrical states of site are original copy in the guide sheet utilizing plane table and alidade after that topographic subtleties are organized on the guide.

Plane Table Surveying

Plane Table Surveying Method :

The guideline of plane postponing is parallelism, implying that the beams attracted from stations to objects on the 

Paper are corresponding to the lines from the stations to the items on the ground. The general places of the 

Items on the ground are spoken to by their plotted situations on the paper and lie on the particular beams. The table is constantly positioned at every one of the progressive stations corresponding to the position it involved at the beginning station. Plane postponing is a graphical strategy for looking over. Here, the field work and plotting are done at the same time and such review doesn't include the utilization of a field book. 

Plane table review is essentially reasonable for filling inside subtleties when navigating is finished by theodolite. At times navigating via plane table may likewise be finished. In any case, this review is suggested for the work where extraordinary exactness isn't required. As the fitting and fixing course of action of this instrument isn't great, most exact work can't be normal.

 Used in Plane Table Survey -

• Plane table

• Alidade for sighting (telescopic or simple)

• Plumb bob and plumb fork

• Compass

• Spirit level

• Chain

• Ranging rods

• Tripod

• Drawing sheet and drawing tools

• Paper clips or screws

Plane Table Surveying

Temporary Adjustments of The Plane Table -

1. Centering : 

This procedure is to determine that the point on the ground is spoken to precisely on the paper. It is completed with the assistance of plumbing fork and plumbing bob.The pointed end (at the high ground) of the pipes fork is kept on paper and at the opposite end, a plumb weave is fixed. The board is moved physically until the weave hangs precisely over the peg of the station. This work can be tedious however an essential for any further exercises.

2. Leveling :

The table is leveled by setting the soul level at various corners and different situations on the table. 

Leveling is done so the planning phase stays corresponding to the ground. It is done in the accompanying three techniques: 

conventional inclining the board 

by ball and attachment game plan or 

by altering the legs of the tripod.

3. Orientation :

The procedure by which the position involved by the board at different overview stations are kept equal is known as the direction. In the plane table reviewing, the entire table should be moved at a few stations to finish a study. Each time the table is moved one needs to ensure that the new station is corresponding to the past one in any case the lines drawn on paper won't speak to similar lines on the field. Techniques for direction are:-

1. Orientation by Magnetic Needle: 

1. This technique is utilized when it is preposterous to expect to cut up the past station from the new station. This strategy isn't a lot of dependable and inclined to mistakes because of varieties of the attractive field.

1. Orientation by Back Sighting: 

1. This is an increasingly solid strategy. In this technique, a specific line drawn from the past station is drawn again from the new station. This procedure is gotten back to locating. One doesn't really need to adhere to a meaningful boundary the subsequent time rather check if the new line superposes over the past one or not.

Methods of Plane Table Surveying -

Radiation :

Strategy It is the easiest technique for plane table studying. This technique is just powerful if the entire reviewing is to be done from one single station for example the table will be in such a situation from where the various purposes of the field are effectively noticeable. The technique is as per the following: 

A point P is to be chosen in such a style, that the various focuses ( A B C D E) are seen effectively from P. 

Focusing, leveling, and direction must be done before looking over. 

From the outset, by putting the alidade on point P a view for station An is to be drawn. 

In the wake of estimating the separation of PA on field, the estimation should be written down to an appropriate scale. 

Also, focuses b, c, d, and e are gotten on paper by drawing views for stations B, C and D and estimating the separations PB, PC, PD and PE on ground individually. 

Focuses a, b, c, d, and e are joined on paper, as appeared in the figure.

Radiation Mothod

Intersection :

Technique In past strategy it was conceivable to gauge each separation on the field physically. In the event of a rocky landscape or harsh surface where separations can't be taken genuinely, it is ideal to utilize crossing point technique. The technique is: 

Two stations O1 and O2 are chosen so the focuses to be situated on paper are effectively observed from them. 

The gauge (o1o2) is plotted on the paper. This is done in the manner underneath: The table can be focused and leveled at station O1 and afterward in the wake of situating at station O2, the separation O1 O2 can be precisely estimated and put up to some scale on the paper. The line o1o2 can be attracted to some scale on the paper and afterward the board can be balanced from station O1 by back locating at station O2. 

From station O1, beams for stations A, B are drawn and so forth. 

Presently moving the table to the new station and situating it again the beams of stations A, B are drawn and so on., 

The convergence of beams from stations O1 and O2 will give focuses a, b and so on paper, as appeared in the figure.

Intersection method

Traversing Method :

This is pretty much like the compass review. It is utilized for running study lines between stations, which have been recently fixed by different techniques for review, to find the geological subtleties. 

The plane table is fixed at an area (state A) 

Starting there, a sight is taken toward B and the separation AB is estimated. 

The plane table is moved to station B and located toward A (this is gotten back to locating). Separation BA was estimated. 

The normal separation among AB and BA are plotted to appropriate scale on the drawing paper. 

At that point the point C is located from B and the separation was estimated. This procedure is rehashed for all the stations. 

Direct some check at uniform spans. At long last, plot the navigate lines on the drawing sheet. Notice that back locating was done distinctly for the initial two stations.

Traversing Method

Resection Method :

This technique is reasonable for setting up new stations at a spot so as to find missing subtleties. It is the way toward deciding the recently plotted situation of any peg station, by methods for sight taken towards known focuses, the area of which has been plotted. 

Resection strategy includes two distinct strategies as follows: 

The three-point issue 

The two-point issue

Compass Traversing Note -- Read

Chain Surveying Note -- Read

 Plane Table Surveying Practical Watch

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                                QUESTIONS AND ANSWER

1 The principle of plane table survey is

= parallelism

2 The plane table is a drawing board size

= 750mm * 600mm

3 What are the different type of alidade?

= plain and telescopic

4 The spirit level is meant for

= leveling

5 What are the different type compass?

= trough compass , circular box compass

6 The north south direction of a 0 mark both ends is

= trough compass

7 The compass is meant for marking the north direction is

= circular box compass

8 The meant for centring the table over a station is

= U-fork with plumb bob

9 Orientation may be done by

= magnetic needle and backsighting

10 The four method of plane table

= radiation, intersection, traversing, resection

11 Single station method of plane table

= radiation

12 The method is suitable for locating inaccessinble points by

= intersection

13 Chain is obstructed but vision free is method

= intersection

14 The method is suitable for connecting by

= traversing method

15 The method is suitable locate missing details by

= resection

16 In plane table survey, the operation which must be carried out is

= orientation

17 The working edge of the alidade is known as

= fiducial edge

18 The north line of the map is marked on the

= right-hand top corner

19 The U-fork and plumb bob are required for

= centring

20 Inaccessible points may be located by the

= intersection

21 The accuracy with which the instrument station can be established is known as

= strength

22 The plane table map cannot be plotted to a different scale, as

= field book

23 The strength of fix is bad if the plane table station is taken

= on the circumference

24 The three point problem can be solved by

= all the methods

25 Intersection method of detailed plotting is most suitable

= plains

26 The two point problem is a method of

= none

27 An alidade is used in plane table surveying for

= drawing line

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Compass Traversing - types of compass ,practical, angels,

                   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.

 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.

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.

Chain Survey Note -- Read 

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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