Surveying system

A surveying system comprising an object to be measured having a retro-reflector and a surveying instrument main body for emitting a distance measuring light and performing a measurement of said object to be measured based on a reflected distance measuring light from said retro-reflector, wherein said surveying instrument main body comprises a distance measuring light projecting module which has a light emitter for emitting said distance measuring light and projects said distance measuring light onto a distance measuring optical axis, a light receiving module which has a photodetector for receiving said reflected distance measuring light and producing a photodetecting signal, a measuring unit which performs a distance measurement of said object to be measured based on said photodetecting signal from said photodetector, an optical axis deflector which has a reference optical axis and deflects said distance measuring optical axis with respect to said reference optical axis, a projecting direction detecting module which detects a deflection angle and a deflection angle direction of said distance measuring optical axis with respect to said reference optical axis, and an arithmetic control module which controls a deflecting action of said optical axis deflector and a distance measuring operation of said measuring unit, wherein said optical axis deflector comprises a pair of optical prisms which are rotatable around said reference optical axis and motors which individually independently rotate said optical prisms, and wherein said arithmetic control module is configured to control a deflection by said optical axis deflector by controlling a rotating direction, a rotating speed, and a rotation ratio of said pair of optical prisms, to perform a two-dimensional scan with said distance measuring light with said distance measuring optical axis as an approximate center, to detect said deflection angle direction of said distance measuring light at a moment of detecting said photodetecting signal during said two-dimensional scan by said projecting direction detecting module, and to control said optical axis deflector in such a manner that the approximate center of said two-dimensional scan moves in said detected deflection angle direction,

• wherein, in a case where two or more photodetecting signals are detected during said two-dimensional scan, said arithmetic control module averages said deflection angle directions detected by said projecting direction detecting module based on each of said photodetecting signals and controls said optical axis deflector in such a manner that said approximate center of said two-dimensional scan moves in an averaged deflection angle direction.