Reading of Angles and Field Book Entry of Measured Angles
In theodolite surveying, accurate reading of angles and proper recording in the field book are essential for reliable results. Surveyors measure horizontal and vertical angles using a theodolite and record them systematically for further calculations and plotting. For ITI Surveyor trainees, understanding this process is very important.
Reading of Angles
Theodolite is used to measure both horizontal and vertical angles. The readings are taken from graduated circles provided in the instrument.
1. Reading of Horizontal Angles
Horizontal angles are measured between two survey lines in the horizontal plane.
Procedure:
- Set up the theodolite and complete temporary adjustments
- Set initial reading to zero or note initial value
- Sight the first point (backsight) and clamp the lower plate
- Rotate the telescope to sight the second point (foresight)
- Read the angle from the horizontal circle
The difference between the two readings gives the horizontal angle.
2. Reading of Vertical Angles
Vertical angles are measured between the line of sight and the horizontal plane.
Procedure:
- Level the instrument properly
- Sight the object through the telescope
- Read the angle from the vertical circle
Vertical angles may be positive (elevation) or negative (depression).
3. Face Left and Face Right Readings
To improve accuracy, readings are taken in two positions:
- Face Left (FL)
- Face Right (FR)
The average of FL and FR readings is taken as the final angle.
Field Book Entry of Measured Angles
Field book is used to record all observations taken during surveying. Proper entry ensures accuracy and easy reference for calculations.
Format of Field Book
| Station | Backsight | Foresight | Face | Angle | Remarks |
|---|---|---|---|---|---|
| A | B | C | FL | 60° | - |
| A | B | C | FR | 62° | - |
Steps for Field Book Entry
- Write date, location, and survey details
- Record station points clearly
- Note backsight and foresight points
- Enter readings for both FL and FR
- Calculate average angle if required
- Add remarks if necessary
Precautions in Recording
- Write entries neatly and clearly
- Avoid overwriting or corrections
- Record values immediately after observation
- Use proper units (degrees, minutes, seconds)
- Verify readings before recording
Common Errors
- Incorrect reading of scale
- Wrong entry in field book
- Ignoring face left/right readings
- Calculation mistakes
Importance in Surveyor Trade
Accurate reading and proper recording of angles are essential for successful surveying. These records are used for calculations, plotting, and preparation of maps.
Conclusion
Reading of angles using theodolite and proper entry in the field book are fundamental tasks in surveying. Careful observation and systematic recording ensure accuracy and reliability.
For ITI Surveyor trainees, mastering these skills is important for professional fieldwork and data handling.