Plane Table SurveyingBranch : civil Engineering (3rd

Sem)

Presented by:

Chikhaliya Khushali .P :151260106007Jain Mayuri .B : 151260106013 Lashwani Nikita .M : 151260106020Mankar Nikita .S : 151260106021Shah Reema .S : 151260106033Contractor Shila .U : 151260106036

Principle:The principle of Plane Tabling is parallelism, meaning that the rays drawn from stations to objects on the paper are parallel to the lines from the stations to the objects on the ground.

Accessories:1) The Plane Table2) The Alidade3) The Spirit Level4) The Compass5) U-fork with Plumb Bob

1) The Plane TableThe plane table is a

drawing boardof 750mm x 600mm size made of well-seasoned wood .

The bottom surface consists of a threaded circular plate for fixing the table on the tripod stand by a wing nut.

2. The Alidade The function of alidade is to

sight objects. There are two types of alidade:

1.Plain Alidade2.Telescopic Alidade

2) The AlidadePlain Alidade:o The plain alidade consists

of a metal or wooden ruler of length about 50 cm.

o One of its edges is bevelled and is known as the fiducial edge.It consists of two vanes at both ends which are hinged with ruler.

o One is known as object vane and carries a horse hair, the other side is called the sight vane and has a narrow slit.

Telescopic Alidade:o The telescopic

alidadde consists of a telescope meant for inclined sight or sighting distant objects clearly.

o This alidade has no vanes at the ends, but is provided with fiducial edge.

3) The Spirit LevelThe spirit level is

meant for levelling the plane table.

The spirit level is a small metal tube containing a small bubble of spirit.

The bubble is visible on the top along a graduated glass tube.

4) The Compass• The compass is meant for marking

the north direction on the map.• There are two types of compass:

1.Trough Compass2. Circular Box Compass

4) The CompassTrough Compass:o The Trough Compass

is a rectangular box made of non-magnetic metal containing a magnetic needle pivoted at the centre.

o This compass consists of a ‘0’ mark at both ends to locate the N-S direction.

Circular Box Compass

o It carries a pivoted magnetic needle at the centre.

o The box is fitted on a square base plate.

o Sometimes two bubble tubes are fixed at right angles to each other on the base plate.

5) U-fork with Plumb BobThe U-fork is a metal strip bent in

the shape of a ‘U’ having equal arm lengths.

The top arm is pointed and the bottom arm carries a hook for suspending a plumb bob.

Orientation:The method of setting up the

plane table at each of the successive stations parallel to the position it occupied at the starting is known as orientation.

There are two methods:1. Orientation by magnetic

needle.2.Orientation by Back

sighting.Orientation by back sighting is

the most preferred and accurate method.

1.Orientation by Magnetic Needle

The north line is marked on the top right corner of the sheet.

When the plane table is shifted from one station to another, the table is oriented with the help of magnetic needle.

The compass is kept along the north line marked on the earlier station, and the table is rotated so that the needle is parallel to the north line.

Then centering and levelling of the table is done, and orientation is completed.

2.Orientation by Back sightingThe table is set up on first station and

next station is bisected with the help of alidade, and line is drawn with appropriate scale.

On moving the table to the next station, the table is orientated with the help of alidade.

The alidade is kept parallel to the previously drawn line, and the table is rotated so as the previous station is bisected along the same line.

Methods of Plane Tabelling

There are four distinct methods of plane tabelling:

1. Radiation2. Intersection3. Traversing4. Resection

1. Radiation:In the radiation method, the

direction of the objects or points to be located are obtained by drawingradial lines along fiducial edge of the alidade after getting the objects or pointsbisected along the line of sight of the alidade.

The horizontal distances are then measured and scaled off on the corresponding radial lines to mark their positions on the drawing.

1. Radiation

2. IntersectionIn intersection method, the objects or

oints to be located are obtained at the point of intersection of radial lines drawn from two different stations.

In this method, the plotting of plane table stations are to be carried out accurately. Checking is important and thus done by taking third sight from another station.

The intersection method is suitable when distances of objects are large or cannot be measured properly. Thus, this method is preferred in small scale survey and for mountainous region.

2. Intersection

3. TraversingThis method is used to plot a

traverse in cases stations have not been previously plotted by some other methods.

In this method stations are first selected. The stations are plotted by method of radiation by taking back sight on the preceeding station and a fore sight to th following station.

3. Traversing

4. ResectionResection is the process of determining

the plotted position of the station occupied by the plane table, by means of sights taken towards known points, locations of which have been plotted.

There are four methods of resection:a. By Compassb. By Back Sightingc. By two point problemd. By three point problem

4. Resection

Two Point ProblemIn this problem, two well defined

points whose positions have already been plotted on the plan are selected. Then, by perfectly bisecting these points, a new station is established at the required position.

Two Point Problem

Three Point ProblemIn this problem, three well defined

points are selected, whose position have already been plotted on map. Then, by perfectly bisecting these three well defined points. A new station is required in order to solve this problem. This is directly placed at the required position. The problem may be solved by following methods:

Bessel’s Method Mechanical Method The trial and error Method

Three Point Problem

Advantages of Plane TabellingIt is simple and cheaper than the

theodolite sirvey.It is most suitable for small scale

maps.No great skill is required to produce a

satisfactory map.It is useful in magnetic areas where

compass may not be used.The mistakes in writing field books

are eliminated.

Disadvantages of Plane TabellingIt is not intended for very

accurate work.It is not suitable in monsoon.It is essentially a tropical

instrument.Due to heaviness, it it

inconvinient to transport.Since there are so many

accessories, there are chances of them being lost.

oErrors in Plane TabellingThe various sources of errors can

be classified as:◦Instrumental errors◦Personal Errors◦Errors in plotting

•Instrumental Errors1. The surface of the table may not be

perfectly leveled.2. The fiducial edge of the alidade might

not be straight.3. The vanes may not be vertical.4. The horsehairs may be loose or inclined.5. The table may be loosely joined on the

tripod.6. The needle of the magnetic compass

may not be perfectly balanced.

• Personal Errors1. Leveling of the table may not be perfect.2. Table may not be centered perfectly.3. Orientation of the table might not be

perfect.4. Table might not be perfectly clamped.5. Objects may not be bisected perfectly.6. Alidade may not be correctly centered on

the station point.7. Rays might not be drawn accurately.8. Alidade may not be centered on the same

side of the paper through out the work.

• Plotting Error1. A good quality pencil with a very

pointef end may not have been used.

2. An incorrect scale may be used by mistake.

3. Errors may result from failure to observe the correct measurement from the scale.

4. Unnecessary hurry at the time of plotting may lead to plotting errors.

Important Points:1. Ground shall be marked as A, B, C..etc.

And points on paper shall be marked as a. b. c.. Etc.

2. The rays from survey stations to the objects shall be drawn by dashed lines.

3. The alidade should be properly pivoted while sighting the objects.

4. The first survey station and the scale of the map shall be chosen such that the entire area can be plotted on the paper.

Important Points:5. While establishing magnetic

north on the paper using trough compass, things causing local attraction shall be kept away of the table.

6. The plane table should be clamped after centering and leveling. The table should rotate at the time of orientation.

THANK YOU