plane table surveying instruments used in plane table surveying method of surveying levelling centering traversing and its types

1. LECTURE-03
TRADITIONAL SURVEY POSITIONAL TECHNIQUES

2. TRADITIONAL SURVEY POSITIONAL TECHNIQUES:
• Traditional survey positional techniques refer to the methods used in land
surveying to determine and establish the positions of points on the Earth's
surface.
• These techniques have been foundational in various fields such as construction,
civil engineering, mapping, and land development.

3. TECHNIQUES
Some of the traditional survey positional techniques include:
1. Plane Table surveying
2. Triangulation
3. Trilateration
4. Total Station
5. Leveling
6. Chain Surveying

4. PLANE TABLE SURVEYING
• Plane table surveying is a traditional method used in land surveying to map and
create plans of relatively small areas directly in the field.
• It involves the use of a plane table, which is essentially a drawing board
mounted on a tripod or stand.
• This method allows surveyors to visually represent the surveyed area and
features by plotting observations and measurements directly onto the drawing
board while working in the field.

5. OBJECTIVE OF PLANE TABLE SURVEYING
• The objectives of plane table surveying include:
o Creating a detailed and accurate map of the surveyed area.
o Establishing control points and reference markers for future surveys or construction projects.
o Determining the distances, angles, and directions between different points on the ground.
o Gathering data for designing infrastructure projects, such as highways, pipelines, and railways.
o Assisting in land management and land development projects.

6. Plane Table Surveying: The Basic Idea Behind It
• Plane table surveying is a method that involves placing a drawing board,
known as a plane table, on the ground and using it as a reference surface.
• The surveyor visually observes and plots the positions of points on the
ground directly onto the drawing sheet.
• By measuring angles and distances, the relative positions of these points
can be determined and mapped accurately.

7. LIST OF INSTRUMENTS USED IN SURVEYING:
• (1) Plane Table
(2) Alidade
(3) Plumbing fork and Plumb bob
(4) Spirit Level
(5) Chain or Tape
(6) Rain roof cover for the plane table
(7) Compass
(8) Ranging Rods
(9) Drawing Sheets
(10) Drawing equipment.

8. DRAWING BOARD
• The drawing board is made up a of well-seasoned wood, so as to
counteract the effect of warping and damages due to weathering.
• The upper surface of the drawing board is kept smooth.
• The table at the center of the underside is attached to the tripod with the
help of a screw and wing nut.
• The table can be clamped in any position using the wing nut.

10. ALIDADE
• An alidade is a straight-edge ruler having some sighting device.
• It is used for sighting objects and drawing lines in Plane Table Surveying. Plane Alidade is
a straight-edge ruler about 450 mm long, made of metal or wood.
• One of the edges is bevelled and graduated.
• The alidade is provided with a sight vane at each end. The sight vanes have hinges at the
lower end so that they can be folded down on the ruler when not in use.
• One of the sight vanes is provided with a narrow slit and is used as an eye vane.

12. ALIDADE
• The object vane is open, and it carries a hair or thin wire at its center. The sight
vanes provide a definite line of sight.
• The line of sight of the alidade is in the same plane as that of the fiducial edge or
in a plane parallel to it.
• Nowadays, Telescopic Alidades are also much in use, in place of Plane Alidades.
When the points too high or low are to be sighted, the accuracy and the range
are considerably increased by providing a telescopic alidade.

13. SPIRIT LEVEL
• The other name used for spirit level is level tube. The essential
condition in plane table surveying is that the board should be
level. This level tube is either tubular or circular.
• It is placed on the board and the bubble is centered in each
position to make the board horizontal.

15. TROUGH COMPASS
• It is one of the vital instruments employed in plane table surveying. Generally, it is 15 cm long and
is provided to plot the magnetic meridian (N-S direction) to facilitate the orientation of the plane
table in the magnetic meridian.
• At the extremities of the trough compass, there are graduated scales with zero at the center and
marking up to 5° on either side of the zero line.
• Longer sides of the trough compass are parallel and plane such that they can be used as a ruler for
drawing the line or for placing the compass such that it coincides with a line already drawn on the
drawing sheet.

17. U-FRAME OR PLUMBING FORK
• A plumbing form is a U-shaped piece of the metal frame. It is used for the
centering of the plane table over the station.
• One end of the frame is pointed and is kept over the drawing sheet
touching the plotted position of the instrument station, while the other
end of the frame carries a plumb bob.
• The position of the plane table is adjusted until the plumb bob hangs over
the station occupied by the instrument

18. U-Frame or Plumbing Fork

19. CONTI…
• The use of a plumbing fork is justified only if the plotting is
done at a large scale and the rays are short.
• Whereas, small-scale mapping, which is usually done with a
plane table, using a plumbing fork is a sheer waste.

20. WATER PROOF COVER
• During rainy days, a waterproof cover is a must so that the
surveying operation can go on without much disturbance.

21. PAPER OR DRAWING SHEET
• The paper or drawing sheet used in Plane Table Surveying
should be of the best quality to withstand rubbing and
scrubbing.

22. Tripod
• An open frame type light tripod is usually used in the simplest
form of plane tables.
• Levelling of the board is achieved with the tripod legs and
checking the horizontality of the board with the help of two spirit
levels fixed at right angles to each other in a block of wood.

23. TEMPORARY ADJUSTMENTS OF PLANE
TABLE:
• Surface of the board should be perpendicular to the vertical axis of
the instrument which can be achieved by placing a spirit level over the
plane table.
• The bevelled Edge of the Alidade should be a straight line which can
be checked by drawing a line along the ruling edge.

24. CONTI….
• The Two Vanes should be perpendicular to the base of the
alidade and can be done by setting the alidade on the corner
edge of a building or on a suspended plumb bob. If they do not
coincide, adjust the hinges till the vane coincides with the plumb
line.

25. LEVELLING
• In plane table surveying, it is the operation of bringing the plane
table in a horizontal plane. Levelling of the board is done with the
help of a spirit level and by employing one of the following methods:
o Tilting of the board ordinarily.
o Adjusting the legs of the tripod.

26. TRIPOD

27. ARRANGEMENT OF PLANE TABLE
SURVEYING EQUIPMENT
• Plane Table Surveying equipment is arranged in 4 steps as follows: -
• Fixing of Plane Table
• Attach the tripod stand to the plane table. Using paper clips or thumb
screws, arrange the drawing sheet on the plane table. From first to last, the
sheet should be in one position.

28. CENTERING
o It is the operation of bringing the plotted station point exactly over the ground
station. A Plumbing Fork is used for centering the plane table.
o First of all, the pointed end of the plumbing fork is kept on the paper while the
other end is attached with a plumb bob.
o It should be noted that exact and proper centering is done only in case of large-
scale mapping. And for small-scale mapping, an error of about 30 cm is
permissible.

29. Levelling
• In plane table surveying, it is the operation of bringing the plane
table in a horizontal plane. Levelling of the board is done with the
help of a spirit level and by employing one of the following methods:
o Tilting of the board ordinarily.
o Adjusting the legs of the tripod.

30. ORIENTATION
o It is the operation of keeping the plane table parallel to the position it occupied at the first station. In such a case, all
the lines plotted will be parallel to the corresponding lines on the ground.
o If the position of the board is different at successive stations, the relative positions of the plotted details will not
remain the same as the relative positions of the details on the ground.
o As a result, the plotted work of the previous stations cannot be connected to that of the successive stations.
o During orientation the table is rotated and the plotted position of the instrument station is also disturbed and shifts
relative to the ground stations.
o Therefore, operations of orientation and centering are therefore interrelated. Orientation of the plane table can be
closed using a trough compass, back sighting.

31. METHODS OF PLANE TABLING:
• (a) Traversing: In this method the location of the Plane Table station is located in
the following manner:
• (1) At previous station a ray is drawn in the forward direction (toward next
station) and point is plotted by measuring the horizontal distance and plotting it to
scale.
• (2) Instrument is shifted to next station (which is just located in first step) and the
previous station is back-sighted to orient the plane table.

32. TRAVERSE
• A traverse is a series of connected lines whose lengths and
directions are to be measured and the process of surveying to
find such measurements is known as traversing. In general,
chains are used to measure length and compass or theodolite
are used to measure the direction of traverse lines.

33. Types of Traverse:
• A Traverse may be of two types. Namely,
1. Open Traverse
2. Closed Traverse

34. 1. Open Traverse
• A traverse is said to be open traverse when the traverse starts
at one point and terminates at another point as shown in the
figure.
• Open traverse is also called as unclosed traverse. It is suitable
for surveying of roads, coastal lines, etc.

35. Closed Traverse
• A traverse is said to be closed traverse when the traverse
formed a closed circuit as shown in the figure.
• In this case, both starting and terminating points of the
traverse coincide with each other. It is suitable for the survey of
boundaries of ponds, sports grounds, forests, etc.

36. CLOSED TRAVERSE

37. METHODS OF TRAVERSING
1. Chain Traversing
2. Compass Traversing
3. Theodolite Traversing
4. Plane Table Traversing