Control unit, surveying instrument, and method of control thereof for improved mechanical stability

A control unit for a surveying instrument, the surveying instrument comprising a base arranged to be mounted on a support structure and a main body arranged to be rotatable about a first axis in relation to said base,

• said control unit being configured to:
• combine at least a portion of a first angle signal representative of an angular position of said main body relative to said base and a portion of a second angle signal representative of an angular position of said main body relative to an external reference to produce a fused angle signal representative of said angular position of said main body relative to said external reference,
• provide a control signal for rotating said main body about said first axis, wherein said control signal is based on said fused angle signal and a desired angular position of said main body relative to said external reference,
• wherein said control unit further comprises:
• a resonance frequency finder configured to estimate at least one resonance frequency associated with said support structure, and
• a filter component configured to selectively apply at least one filter on said control signal, said fused angle signal, or said first angle signal, wherein an applied filter is configured to filter out a corresponding respective resonance frequency associated with said support structure estimated by said resonance frequency finder.