BIRLA VISHWAKARMA MAHAVIDYALAYA SUB : SURVEYING TOPIC : PLANE TABLE SURVEYING Presented by Khushbu Patel(130070106087) Snehal Patel(130070106094) From S.Y.B.E.(CIVIL) Batch : A2

CONTENT Introduction Principle of plane tabling Instrument used Methods of orientation References

INTRODUCTION Plane tabling is graphical method of surveying. In plane table surveying a plane table is used for taking the measurement and for plotting the plan in the field. A plane table consist of a drawing board mounted on a tripod. Plane table surveying is a method in which the field work and plotting are done simultaneously.

Introduction continue… Plane table survey is mainly used for small scale and medium scale mapping an open area where great accuracy is not required. It is also used for plotting the topographical maps in the field. It is also suitable for filling in interior details when traversing is done by theodolite.

PLANE TABLE

PRINCIPLE OF PLANE TABLIG The principle of plane tabling is parallelism , meaning that the rays drawn from ground stations to objects on the drawing sheet are parallel to the lines from the ground stations to the objects on the ground . The relative positions of the objects on the ground are represented by their plotted positions on the drawing sheet and lies on the respective rays.

Principle of plane and tabling continue… The table is always placed at each succecive stations parallel to the position it occupied at the starting station. The plane tabling may be defined as graphical construction of straight lines , angles and triangles for plotting the ground detail points.

INSTRUMENT USED There are main five instruments used in plane tabling. Plane table Alidade Spirit level Trough compass U- fork or plumbing fork

Instrument used continue… (1) Plane table : The plane table consist of a drawing board made of well-seasoned wood , such as teak or pine. The size of the board is generally 750mm*600mm. The thickness of the board is about 20mm. The bottom surface consist of a threaded circular plate for fixing the table on the tripod stand by a wing nut.

Instrument used continue… (2)Alidade : An alidade is a straight – edge ruler having some sighting device. It is used for sighing the objects and drawing the rays . The ray should be drawn along fiducial edge. Alidade are of two types.1. plain alidade 2. telescope alidade.

TELESCOPIC ALIDADE

Instrument used continue… (3) Spirit level : The spirit level is a small metal tube containing a small bubble spirit. The level tube is either of the tubular type or of the circular type. The base of the level tube is flat so that it can be laid on the table. The spirit level is meant for levelling plane table.

SPIRIT LEVEL

Instrument used continue… (4) Trough compass : The compass used with a plane table is a trough compass in which the longer sides of the trough are parallel and flat so that either side can be used as a ruler or laid down to coincide with a straight line drawn on the paper. The compass is a rectangular box made of non – magnetic metal containing a magnetic needle pivoted at the centre.

Trough compass

Instrument used continue… (5) U – fork : The U- fork is a metal strip bent in he shape of a ‘U’ having equal arm length. The top arm is pointed and the bottom arm carries a hook for suspending a plumb bob. It is used for two purposes 1. Transferring of the ground point 2. centering the table.

PLUMB BOB

METHODS OF ORIENTATION There are two methods of orientation : (1)orientation by magnetic needle (2) orientation by backsighting Orientation by magnetic needle : This method is suitable when local attraction is not suspected in the area. To orient the plane table at subsequent stations , the trough compass is placed on the paper with its edge along the line representing the magnetic meridian.

Methods of orientations continue… (2) Orientation by backsighting : This method is accurate and is always preferred. In this method , the plane table is oriented by backsighting on the previous station. The backsighting process is always preferred , because it is reliable. Duirng orientation , it should be always remember that the requirements of centering , levelling and orientation must be satisfied simultaneously.

REFERENCES Surveying, R.B.Khasiya,5th Edition. www.slideshare.net/.../plane-table surveying http://en.m.wikipedia.org

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