A turning point is the point selected on the route before shifting the instrument. The change point is also called a turning point. The staff is kept on the turning point and a foresight is taken before shifting the instrument. The staff should not be moved when the instrument is being shifted. After the instrument has been shifted and setup at the new location , a backsight is taken on the staff still held at the change point.

Sights on a Turning Point

Sights on a turning point in surveying refer to the measurements taken to determine the position and elevation of a point that is not directly visible from the instrument station. These sights are usually taken using a theodolite or total station, and they involve measuring the angles and distances between different points.

The question asks which sights are taken on a turning point, and the correct answer is option C, which states that both foresight and backsight are taken. Let's break down why this is the correct answer:

Foresight
- A foresight is a measurement taken from the instrument station to a point that is visible from the station.
- In the case of a turning point, the foresight is taken to a point that is not directly visible from the station, but can be seen from another point that is visible.
- The foresight is used to determine the position of the turning point relative to the instrument station.

Backsight
- A backsight is a measurement taken from a point that is visible from the instrument station to the instrument station itself.
- In the case of a turning point, the backsight is taken from the point that can see the turning point to the instrument station.
- The backsight is used to determine the orientation of the instrument station relative to the turning point.

Intermediate Sight
- An intermediate sight is a measurement taken between two points that are both visible from the instrument station.
- In the case of a turning point, an intermediate sight may be taken between the instrument station and a point that is visible from both the station and the turning point.
- However, an intermediate sight is not necessary for determining the position and elevation of the turning point, so it is not included in the correct answer.

Therefore, the correct sights to be taken on a turning point are foresight and backsight.

C