Auto centering levelling

A surveying system can include a surveying instrument, a control system, a tilt measuring system, a levelling unit, a camera system, and a second distance meter, wherein the control system is configured for obtaining an image position of a captured image, adjusting a tilt status until a first tilt status is obtained, the second distance meter aiming onto the location on the ground in the first tilt status, determining the first tilt status, effecting the second distance meter to measure a distance to the location on the ground, effecting a first angle encoder to measure a rotatory position of a support unit, effecting the levelling unit to adjust the tilt status, and calibrating a preconfigured centre point based on the distance to the location on the ground, a deviation between the first tilt status and the second tilt status, and/or the rotatory position of the support unit.