Monday, August 19, 2013

Plane Table Survey - Surveying(Civil Engineering)


Hi,

A short introduction to Plane Table Survey- A graphical method of Surveying.



Plane Table Survey:


Plane Table Survey is a method of plotting the plans on the sheet, in which field work and the office work are done simultaneously. It is also known as the graphical method of Surveying. Therefore the main characteristic of the map is that, there is no need of carrying a field book to note various readings.




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.



Procedure: 
To perform the plane table survey one has to follow the following procedure at every plane table set-up at various stations.

(a) Fixing the plane table to the tripod stand
(b)Setting up and temporary adjustments:
  1.     Leveling the plane table with the help of spirit level
  2.    Centering with the help of plumbing fork
  3.     Orientation by trough compass or by back sighting

  • (c) Sighting the points with the help of Alidade


Methods of plane tabling:


1. For locating details: 

(a) Radiation Method: 
With the help of Alidade, a ray is drawn towards the point. Then using the Chain or Tape the horizontal distance is measured from the Plane Table to the point. Then using the scale of plotting, this point is located on the sheet.

(b) Intersection Method: 
In this method no chain or tape is needed, just two instrument stations are needed. Intersecting rays are drawn from these two stations whose location is already plotted on sheet(by measuring the distance between them). The point of intersection of the two rays is the location of the point of interest.


2. For locating Plane Table Stations: 
(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.


(b) Resection: 
Resection is the process/method of finding the position of a station where plane table is placed. Sights are taken towards the known and visible points and rays are plotted.

Procedure :
First of all the plane table is oriented correctly by one of the four given methods:
(1) Orientation by trough compass
(2) Orientation by back sighting
(3) Orientation by two point problem
(4) Orientation by three point problem

Then afterwards point is located.

Thank You!

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