Short Answer:

The sources of errors in theodolite surveying are mainly due to the instrument, the observer, and the surroundings. These errors affect the accuracy of angle measurements and can lead to wrong results if not properly controlled.

Common sources include improper leveling, misalignment of the telescope, parallax error, incorrect reading, wind, heat, and ground vibrations. Errors can be reduced by careful setup, skilled operation, and repeating measurements using methods like the repetition method.

Detailed Explanation

Sources of errors in theodolite surveying

In theodolite surveying, the goal is to measure horizontal and vertical angles with high accuracy. However, several types of errors can occur during the process. These errors can be caused by faults in the instrument, mistakes made by the observer, or outside environmental conditions. Identifying and minimizing these errors is important to get reliable results in surveying work.

1. Instrumental errors
   These errors happen because of defects or imperfections in the theodolite.

• Collimation error: If the line of sight is not exactly aligned with the telescope’s axis, the measured angle may be wrong.
• Graduation error: If the angle scale is not marked correctly or has uneven divisions, the reading will be incorrect.
• Vertical axis not truly vertical: If the instrument is not leveled properly, the vertical axis may tilt and cause angular errors.
• Loose or worn parts: If clamps, screws, or other parts are loose or worn out, they can shift during measurement.

2. Personal (observational) errors
   These are caused by the person using the theodolite.

• Parallax error: Happens when the image and crosshairs are not focused properly. The observer may read a wrong angle.
• Incorrect reading: Misreading the scale or noting the wrong number leads to recording errors.
• Poor centering or leveling: If the instrument is not placed exactly above the station point or not leveled properly, all measurements will be affected.
• Improper use of clamps: Not locking the clamps before reading can cause the instrument to move slightly.

3. Natural (environmental) errors
   These occur due to weather, ground conditions, or surrounding objects.

• Wind: Strong wind can shake the instrument or the tripod, especially on open ground.
• Sun and heat: Direct sunlight can cause expansion in the metal parts of the instrument, changing its shape slightly and affecting accuracy.
• Uneven ground or vibration: If the ground is soft or vibrating, the instrument may not stay stable.
• Visibility problems: Fog, dust, or glare from sunlight can make sighting targets difficult.

How to reduce these errors:

• Carefully level the instrument before starting work.
• Always check for parallax and adjust the focus correctly.
• Repeat angle measurements and use averaging methods like the repetition method.
• Keep the instrument clean and maintain it regularly.
• Choose stable ground and work in calm weather if possible.
• Avoid direct sunlight on the instrument during long measurements.

Even the best instrument cannot give perfect results if handled carelessly. A good surveyor always checks everything before recording the final reading.

Conclusion

Errors in theodolite surveying come from the instrument, the user, or the environment. By knowing their sources and taking care during setup and observation, surveyors can reduce these errors and get more accurate and reliable results in the field.