Introduction

Profile levelling is a method of surveying that has been carried out along the central line of a track of land on which a linear engineering work is to be constructed/ laid. The operations involved in determining the elevation of ground surface at small spatial interval along a line is called profile leveling.

Principle

Simple addition and subtraction is used to determine the elevations of various points.

Equipments Used

1) Auto level with tripod.
2) Graduated Staff.
3) Measuring Tape.

Dos and Don'ts

Dos

1. Center and level the base of plane table accurately.
   
2. Crosshairs must be focused sharply.
   
3. Keep the backsight and foresight distances nearly equal to compensate for collimation error, if any.
   
4. Always take 3 or more observations of each point to take the average.
   
5. Take sufficient number of observations at regular interval along and across the direction of survey, so as to represent the ground profile (longitudinal and cross-sectional) accurately.
   
6. In profile levelling, use Height of Instrument Method for computation of RI's.
   
7. Apply checks after computing RI's.
   
8. Find closing error and distribute it.
   
   

Don'ts

1. Handle the Auto Level with utmost care. If dropped accidently, it may damage compensator and digital display.
   
2. If using aluminum staff, be away from electric poles, transformers and wires.
   
3. While shifting the instrument from one station to another station, always keep it in box for transport.
   
4. Protect the instrument from heavy rains.