There are four methods of surveying with the plane table.
1. Radiation: It is used for locating the details from stations, which have been previously established by other methods of surveying such as triangulation or transit type traversing.
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| Radiation Method Of Plane Table |
In this method, the point is located on the plan by drawing a ray from the plane table station to the point, and plotting to the scale along the ray the distance measured from the station to the point. The method is suitable for the survey of the small areas which can be commanded from a single station.
Procedure:
>Select a point P so that all points to be located are visible from it.
>Set up the table at P and after leveling it, clamp the board.
> Select a point p on the sheet so that it is exactly over the station P on the ground by the use of a U frame. The point represents on the sheet the instruments station P on the ground.
> Mark the direction of the magnetic meridian with the help of the compass in the top corner of the sheet.
>Centring the alidade on p, sight the various points, A, B, C, etc, and draw rays along the fiducial edge of the alidade lightly with a chisel pointed pencil.
>Measure the distances PA, AB, AC, etc, from P to the various points with the chain or tape, or by stadia and plot them to scale along the corresponding rays. Join the points a,b,c, etc, to give the outline of the survey.
NOTE:- The fieldwork can be checked by measuring the distances, AB, BC, CD, etc,
2. INTERSECTION: In this method, the point is fixed on the plan by the intersection of the rays drawn from the two instruments station. The line joining these stations is called the baseline.
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| Intersection Method Of Plane Table |
i. select two points P and Q on the ground so that visible each other.
ii. Set the table at P and level and mark the magnetic north on the paper with the help of a compass.
iii. Alidade kept on p sight the objects Q, A, B, C, D, E, and F and draws the rays along the fiducial edge of the alidade towards Q, A, B, C, D, E, F.
iv. Measure the Pand Q and mark the point q with a suitable scale on the paper along the line drawn pq.
v. Shift the table on Q and center the table so that q is exactly over Q. Orient the table by backsighting P and clamp the table.
vi. With the alidade touching q.sight the same object and draws rays.The intersection of determining the position of A, B, C, etc.
3.Traversing method:-This method is similar to the closed traverse method. It is used for locating the details between the stations which is fixed by another method of surveying. This method is also used in a topographical survey.
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| TRAVERSING METHOD OF PLANE TABLE |
Procedure:-
i. Set the plane table at station A. Make the center and level then board clamped.
ii. Mark the magnetic meridian on the sheet.
III. Centre the alidade on point a sight the station B and measure the length of AB and draw the rays on a suitable scale on the sheet ab with the edge of alidade.
iv. Locate the details by the use of the radiation method or offset method.
v.Set the plane table on station B. Orient the table and backsight to A then sight the station C.
Measure the length BtoC and draw the line bc on a previous use scale.
vi. Continue the process until all the remaining stations are plotted.
vii. It can be also checked from the sighting stations or A to C and B to D or B to E.
4. Resection Method.
This method is used for establishing the instrument stations or after completing the traverse surveying the important object cannot be located due to difficulties and missed the station.
PROCESS:-
i.Select the two stations P and Q on the ground and measure the length PQ and plot to a scale pq on a suitable scale.
ii. Set the table at P , Centre, and level the table so that the point p is over the P.
iii. Place the alidade along pq, orient the table by turning the board until the signal at Q is bisected, and then clamp it.
iv. With the alidade touching at p sight the station R and draw a ray p to r.
v. Shift the table at R. and make the center and level and sight the point P by back sighting and clamp the table.
vi. With the alidade centered on q, sight the station Q and draw a ray. The point of intersection of this ray and that previously drawn from p gives the required point r.
See ALso
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