Detail plotting by radiation method.

Introduction

In the radiation method of plane table surveying, the direction of the objects or points to be located are obtained by drawing radial lines along fiducial edge of alidade after getting the objects or points bisected along the line of sight of the alidade.
This experiment is useful to study detail plotting by radiation method.

Principle

  1. It makes use of a distance and a direction to locate the object.
  2. The positions of the points are plotted on the paper by measuring the distances to the different objects using a tape and by plotting these distances to a scale along the rays drawn to the respective objects using alidale.


Equipments Used

  1. Plane table with tripod.
  2. Alidade.
  3. Plump bob.
  4. Plumbing fork.
  5. Ranging rods.
  6. Spirit level tube.
  7. Drawing sheet.
  8. Level with tripod.
  9. Leveling staff.
  10. Magnetic compass.
  11. Measuring tape.
  12. Graticule.
  13. Clinometer.
  14. Theodolite.
  15. Staff.

Dos and Don'ts

Dos

  1. Center and level the base of plane table accurately.
  2. Don't forget to orient the plane table with respect to magnetic north.
  3. Always use good quality drawing sheet for mapping purpose.
  4. Drawing sheet must be firmly pasted on plane table to avoid any wrinkles.
  5. Make a diagonal scale and use it for plotting the distances so as to compensate expansion or shrinkage of drawing sheet.
  6. Bisect the ground object accurately using alidade.
  7. Measure the long distances with measuring tape.
  8. This method is accurate than intersection method but slower.



Don'ts

  1. Don't measure the long distances with measuring tape. Instead use tacheometric method to get long distances.
  2. Don't waste too much of time to carryout exact centering of plane table, particularly in hilly area. It should be set close by within the plotting accuracy limit.
  3. Ignore plotting the fields having dimensions less than the plotting accuracy.
  4. Don't use this method in plain and small areas.



Observations

  1. All the objects in the area are plotted in the same manner.
  2. The work is completed in continuation of the area.
  3. Sufficient elevation measurements are taken during work.