These slides deal with the techniques and methods of the plain table survey. Graphical method of surveying in which the fieldwork and plotting are done simultaneously.

1. PIYUSH KUMAR
ASST. PROFESSOR
PLANE TABLE SURVEYING

2. PLANE TABLE SURVEYING
 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 and
2. A straight edge called an alidade.

3. PLANE TABLE SURVEYING

4.  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.
THE DRAWING BOARD
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.
 One of the vanes known as sight vane is provided with a narrow slit with three holes, one at
the top, one at the bottom and one in the middle.

5. PLAIN ALIDADE
Sight Vane
Object Vane
Fiducial Edge
5

6. 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.

7. SPIRIT LEVEL

8.  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 of the station
location on the table over its ground position.
PLUMBING FORK
PLUMBING FORK
Plumbing Fork

9. i) It is most suitable for preparing small-scale maps.
ii) It is most rapid.
iii) The field book is not necessary as plotting is done in the field concurrently with the field
work, and hence the mistakes in booking the field notes are avoided.
iv) The surveyor can compare the plotted work with the actual features of the area surveyed
and thus can ascertain if it represents them properly.
v) It is particularly advantageous in magnetic areas where compass survey is not reliable.
vi) It is less costly than a theodolite survey.
vii) No great skill is required to prepare a satisfactory map.
ADVANTAGES OF PLANE TABLING

10. i) It is not suitable for work in a wet climate.
ii) It is heavy, cumbersome and awkward to carry.
iii) There are several accessories to be carried, and, therefore, they are likely to be lost.
iv) It is not intended for accurate work.
v) If the survey is to be re-plotted to a different scale or quantities are to be computed, it is
a great inconvenience in absence of the field notes.
DISADVANTAGES OF PLANE TABLING

11.  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.
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 disleveling of the plane table, throws the
location of the point considerably out of its true location.

12.  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
ORIENTING THE PLANE TABLE

13. ORIENTING BY MAGNETIC NEEDLE
 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.
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.

14. There are four methods of surveying with the
plane table:
1. Radiation Method
2. Intersection Method
3. Traversing Method
4. Resection Method
METHODS OF PLANE TABLING

15. RADIATION METHOD
 In this method the objects are located by radiating lines from the point, and
measuring the distance with chain or tape with suitable scale. It is chiefly used for
locating the details from the station, which have been established previously by
other methods triangulation, or traversing.

16. INTERSECTION METHOD
 In this method the point is fixed on the plane by the intersection of the rays
drawn from the two instrument stations. The line joining the stations is called
Base line. The method requires only the linear measurements of this line.

17. TRAVERSING METHOD
 This is similar to that of Compass Survey or Transit Traversing. It is used for
running survey lines between stations, which have been previously fixed by other
methods of survey, to locate the topographic details. It is also suitable for the
survey of roads, rivers, etc.

18. RESECTION METHOD
 This method is used for establishing the instrument stations only. After
fixing the stations, details are located either by radiation or intersection.

19. ERRORS IN PLANE TABLING
 Following precautionary measures should be taken while performing field
work:
o The table must be accurately oriented once the table is shifted.
o The alidade should be correctly centred on the station point on paper.
o The expansion and contraction of paper should be taken care off.
o The table should accurately centred.
o The rays should be accurately drawn through the station points.
o Table should be sufficiently clamped.
o The board should be horizontal.
o The objects should be accurately sighted.