1. Civil Department

2. GROUP MEMBERS GROUP MEMBERS:- ENROLLMENT NO. NAME OF THE STUDENT 130410106001BURHAN ADENWALA 130410106002PRIYANK AGRAWAL 130410106003TAMANNA BADAR

3. PLANE TABLE SURVEYING Sardar Vallabhbhai Patel Institute Of Technology/Vasad SURVEYING

4.  Plane Tabling is a graphical method of surveying in which the field work and plotting are done simultaneously.  Useful to fill in details between stations fixed by triangulation or theodolite traversing.  Particularly adapted for small scale or medium scale mapping in which great accuracy in detail is not required.  The plane table consists essentially of: 1. A drawing board mounted on a tripod stand and 2. A straight edge called an alidade. PLANE TABLE SURVEYING

5. Setting of Plane Table

6. THE DRAWING BOARD  Made of well-seasoned wood such as teak or pine.  Size varies from 40cm x 30cm x 75cm x 60cm or 50cm to 60 m square.  It is mounted on a tripod in such a manner that it can be leveled, and revolved about a vertical axis and clamped in any position.

7. PLAIN ALIDADE  Consists of a metal (brass or gunmetal) or boxwood straight edge or ruler about 50 cm long.  The beveled (ruling or working) edge of the alidade is called the fiducial edge.  It consists of two vanes at the ends, the vanes are hinged and can be folded when the alidade is not in use.  One of the sight vanes is provided with a narrow slit and the other with a central vertical wire or hair. Both the slits thus provide a definite line of sight which can be made to pass through the object to be sighted.  A plane alidade can be used only when the elevations of the of the objects are low. 

8. PLAIN ALIDADE Object Vane Sight Vane Fiducial Edge 8 Line of sight

9. TELESCOPIC ALIDADE  The alidade which is fitted with a telescope is known as a telescopic alidade.  It is used to take inclined sights.  It increases the range and accuracy of the sights.  It consists of a small telescope with a level tube.  A graduated scale is mounted on the horizontal axis.  One side of the metal ruler is used as the working edge along which lines are drawn.  The angles of elevation or depression can be read on the vertical circle.

11. SPIRIT LEVEL  It consists of a small metal tube which contains a small bubble.  The spirit level may also be circular but its base must be flat so that it can be laid on the table.  The table is truly level when the bubble remains central all over the table.

12. THE TROUGH COMPASS  A trough compass consists of a magnetic needle pivoted at its centre freely.  It is used for orienting the plane table to magnetic north.  The edges of the box compass are straight and the bottom is perfectly flat.  When the freely suspended needle shows 0 ⁰ -0 ⁰ readings at each end, a line is drawn on the drawing paper which represents the magnetic North.

14. PLUMBING FORK  The plumbing fork consists of a hair pin-shaped brass frame, having two equal arms.  One end has a pointer while a plumb bob is attached the other end.  It is used in large scale survey for accurate centering the table over the point or station or occupied by the plane table when the plotted position of that point is already known on the sheet. It is also used for transferring the location of the instrument station on the sheet on to the ground. The fork is placed with its upper arm lying on the top of the table and the lower arm below it. The table is said to be centered when the plumb bob hangs freely over ground mark.

15. SETTING UP THE PLANE TABLE  The table should be set up at a convenient height. (say about 1m). The legs of the tripod should be spread well apart, and firmly fixed into the ground.  The table should be so placed over the station on the ground that the point plotted on the sheet corresponding to the station occupied should be exactly over the station on the ground. This operation is known as the centering of the table. This may be done using a plumbing fork or U frame.

16. SETTING UP THE PLANE TABLE  In this operation, the table top is made truly horizontal. For rough and small scale work, leveling can be done by eye estimation whereas for accurate and large scale work, leveling achieved with an ordinary spirit level. The leveling is specially important in hilly terrain where some of the control points are situated at higher level and some other at lower level. The dislevelling of the plane table, throws the location of the point considerably out of its true location.

17. ORIENTING THE PLANE TABLE  The operation of keeping the table at each of the successive stations parallel to the position which it occupied at the first station is known as orientation. It is necessary when the instrument has to be set up at more than one station. There are two methods of orienting the table: 1. Orientation by the Magnetic Needle 2. Orientation by Backsighting

18. ORIENTING BY MAGNETIC NEEDLE  In this method, magnetic north is drawn on paper at a particular station. At the next station trough compass is placed along the line of magnetic north and the table is turned in such a way that the ends of magnetic needle are opposite to zeros of the scale.  The board is then fixed in position by clamps.  This method is used when it is not possible to bisect the previous station from the new station.  This method is not much reliable and prone to errors due to variations of magnetic field.

19. ORIENTING BY BACKSIGHTING  In this method the table is orientated by back sighting through the ray which is drawn from the previous station. This is the most accurate and reliable method of orientation of plane table.