What are control points in surveying?

A control point is a point on the ground, or it is a point on any permanent structure whose horizontal and vertical distance or direction is known this point is known as control point.

Control point is used as a starting point of the survey work.

There are three type of control point

1. Primary
2. Secondary
3. Tertiary

1. Primary: It is the network of control point co-ordinated in all three dimensions to give fixed overall reference framework for the works.

• These are the main control points fixed from national reference points.
• Its form a closed loop.
• Built in redundancies for checking
• Set out by specialist surveyors
• Position and level know

2. Secondary: It is the local control points for construction or baselines established.
Set out from the primary control point.

• Set out from the primary control point
• It is forming the control points for setting out base lines & sites grids.
• May have associated level value

3. Tertiary: It is the points set out at the actual position for construction or at suitable offset positions.

• Set out so dimensional checks can be made.
• These are the points you will be setting out relate to construction elements.