1. Unit 4. Plane Table Surveying

2. Unit 4: Plane table surveying
Topics covered
Definition, general accessories of P.T., operations of P.T.
Orientation - by compass, by back sighting
Methods of plane tabling - Radiation, Intersection, and Traversing.
Advantages & Disadvantages of plane table surveying.
Errors in P.T.
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Unit 4: Plane table surveying

3. 4.1 Definition, Accessories & operation of P.T.
What is plane table surveying?
Graphical method of surveying
Skips one intermediate steps of recording measurement
Where it fits?
For detailing purpose once the traverse is laid out
Speed is important than accuracy
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Unit 4: Plane table surveying

4. Unit 4: Plane table surveying
4.1 Accessories of P.T.
Plane table
Traverse (small in size)
Johnson ( 45×60 cm or 60×75 cm )
Ball & socket joint
Upper & lower screw
Survey coast
For precise work
Levelling through foot screw
Clamp & tangent screw
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Unit 4: Plane table surveying

5. Unit 4: Plane table surveying
4.1 Accessories of P.T.
Alidade
Pain alidade
For ordinary survey
Limitation in slope
Alidade
Telescope alidade
Superior quality
Telescope used to sight
For accurate surveying
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Unit 4: Plane table surveying

6. Unit 4: Plane table surveying
4.1 Accessories of P.T.
Plumbing fork
Centring purpose
Consists of hair pin –shaped light metal frame
Spirit level
To ascertain if the table is properly levelled
Place the level in two different position perpendicular to each other
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Unit 4: Plane table surveying

7. Unit 4: Plane table surveying
4.1 Accessories of P.T.
Trough compass
Used for orientation purpose
Drawing paper
Should be superior quality
For precise work, two sheets are mounted with their grains perpendicular to each other
For very precise work, fibre glass sheet is used
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Unit 4: Plane table surveying

8. Unit 4: Plane table surveying
4.1 Operation of P.T.
P.T. surveying involves 3 steps of operation
Fixing
Setting
Levelling the table
Centring
Orientation
Sighting the points
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Unit 4: Plane table surveying

9. Unit 4: Plane table surveying
4.2 Operation of P.T.
Orientation
Process of putting table such that the direction of line on table is parallel to that in the ground
Essential condition when there is more than one station
Orientation disturbs the centring
For precise work, repetition of orientation and shifting of table is necessary
Methods
By trough compass
By back sighting
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Unit 4: Plane table surveying

10. Unit 4: Plane table surveying
4.2 Operation of P.T.
Orientation by trough compass
Less accurate method
Used when there is no second point for orientation
When speed is more important than accuracy
For approximate orientation prior to accurate orientation
Orientation by back sighting
Precise method of orientation
Sighting the points
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Unit 4: Plane table surveying

11. 4.3 Methods (Systems) of Plane Tabling
Radiation
Intersection
Traversing
Resection
The first two methods for locating details whereas second two for locating plane table station
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Unit 4: Plane table surveying

12. 4.3 Methods (Systems) of Plane Tabling
Radiation
Suitable
when one single station can control the details to be located
When distance between the station and details are short.
Wider scope if distance can be computed tacheometrically with telescope alidade.
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Unit 4: Plane table surveying

13. 4.3 Methods (Systems) of Plane Tabling
Intersection (Graphic triangulation)
Used when distance between station and details is either too long or can’t be measured accurately.
Needs at least two plane table station
Only base line is measured
Details are plotted by intersection of rays.
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Unit 4: Plane table surveying

14. 4.3 Methods (Systems) of Plane Tabling
Traversing
Same as radiation but locate the survey station
If there are n number of station, plane table will have to be set on at least (n-1)stations to know the error of closure
The traverse can be completed even by setting on (n-2) stations
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Unit 4: Plane table surveying

15. 4.4 Advantages and disadvantages of Plane Table surveying
No possibility of omitting the necessary measurements
Enables comparision of map and ground on the spot
Less distance measurement
No chance of data recording mistakes
Useful in magnetically influenced zone
Simple, cheaper than other methods
No high skill required for job
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Unit 4: Plane table surveying

16. 4.4 Advantages and disadvantages of Plane Table surveying
Inconvenience for reproduction of map in different scale
Not accurate method of survey
Can’t be used in rainy and wet climate
Use of many equipment.
Heavy equipment, inconvenient to transport
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Unit 4: Plane table surveying

17. 4.5 Errors in Plane Tabling
Error depends upon several factors
Quality of instruments available
Speed of work aimed
Character of survey
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Unit 4: Plane table surveying

18. 4.5 Errors in Plane Tabling
Sources of errors
Instrumental
Errors of plotting
Personal
Non-horizontality of table
Defective sighting
Defective orientation
Inaccurate centring
Movement of board between sighting
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Unit 4: Plane table surveying

19. Thank you for your attention!
Any questions? Querries?
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Unit 4: Plane table surveying