Monday, August 19, 2013

Plane Table Survey - Surveying(Civil Engineering)


A short introduction to plane tabling- A graphical method of Surveying.

Plane Table Survey:

Plane Table Survey is a method of Surveying in which field work and the office work are done simultaneously. It is also known as the graphical method of Surveying. A manuscript map is made in the field and the topographic details can be filled in later.

Plane-Table Cut-a-way, shows a part of the table and the tripod stand

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 do the plane tabling one has to follow the following procedure at every plane table set-up:

  • (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: A ray is drawn towards the point with the help of the Alidade.  With the help of Chain or Tape the horizontal distance is measured from the Plane Table to the point and this point is located on the sheet by plotting it into the scale of the map.

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

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 the process of finding the position of a station where plane table, is placed, with the help of sights taken towards known and visible points whose location has already been plotted.

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!

Note: If reader want details of any of the topic please, leave a comment below.
Ref: GATE - 2013 (GK Publishers )


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