Aquaculture Engineering (2+1)

Methods of plane tabling - Radiation

Unit 1- Surveying

Plane table surveying
Working operations

Methods of plane tabling

Radiation

In this method, a ray is drawn from the instrument station towards the point, the distance is measured between the instrument station and that point, and the point is located by plotting to some scale the distance so measured. This method is more suitable when the distances are small and one single instrument station can control the points to be detailed.
The following steps are necessary to locate the points from an instrument station T.

• Set the table at T, level it and transfer the point on to the sheet by means of plumbing fork, thus getting “t” representing T. Clamp the table.
• Keep the alidade touching “t” and sight to A, draw the ray along the fiducial edge of the alidade. Similarly sight different points B, C and D, E etc., and draw the corresponding rays (A pin may be inserted at “t” and the alidade may be kept touching the pin while sighting the points)
• Measure TA, TB, TC, TD, TE etc., in the field and plot their distance to some scale along the corresponding rays, thus getting a, b, c, d, e etc., Join these if needed.