Surveying instrument

1. A surveying instrument comprising a monopod which is installed on a reference point, a surveying instrument main body which is provided at a known distance from a lower end of said monopod and a known angle with respect to an axis of said monopod and has a reference optical axis, two auxiliary legs which extend downward from a middle portion of said monopod at a predetermined angle, and a lower image pickup module which is provided at a known position with respect to said surveying instrument main body, wherein said surveying instrument main body comprises a measuring unit configured to measure a distance to an object to be measured, a measuring direction image pickup module configured to acquire an observation image including said object to be measured in a predetermined relationship with said reference optical axis, and an arithmetic control module configured to make said measuring unit for measuring a predetermined measuring point, make said measuring direction image pickup module for acquiring an image of said object to be measured, and make said lower image pickup module for acquiring a lower image, wherein said surveying instrument main body is supported by three points by said monopod and said auxiliary legs, and a positional change or a rotational change of said surveying instrument main body is calculating based on a change of said lower image, wherein said monopod comprises a reference plate provided at said lower end of said monopod, a reference target provided on an upper surface of said reference plate, and a ferrule provided on a lower surface of said reference plate in such a manner that a center of said reference target coincides with an axis, wherein said lower image is acquired in such a manner that said reference target and at least one reference object are included, and said arithmetic control module calculates a rotation angle of a longitudinal direction and a rotation angle of a lateral direction of said surveying instrument main body based on a displacement of a position of at least one of said reference target and said reference object in said lower image.

2. The surveying instrument according to claim 1 , wherein said monopod is configured expandable or contractible.

3. The surveying instrument according to claim 2 , wherein a leg length reference line is set in said lower image, and said arithmetic control module calculates an expansion or contraction amount of said monopod based on a distance between said leg length reference line and a lower end of said reference plate in said lower image.

4. The surveying instrument according to claim 3 , wherein said surveying instrument main body further comprises an attitude detector configured to detect the tilts of two axes with respect to the horizontality, and said arithmetic control module converts a rotation angle of a longitudinal direction and a rotation angle of a lateral direction of said surveying instrument main body into a vertical angle and a horizontal angle based on a detection result of said attitude detector.

5. The surveying instrument according to claim 2 , wherein said surveying instrument main body further comprises an attitude detector configured to detect the tilts of two axes with respect to the horizontality, and said arithmetic control module converts a rotation angle of a longitudinal direction and a rotation angle of a lateral direction of said surveying instrument main body into a vertical angle and a horizontal angle based on a detection result of said attitude detector.

6. The surveying instrument according to claim 1 , wherein said surveying instrument main body further comprises an attitude detector configured to detect the tilts of two axes with respect to the horizontality, and said arithmetic control module converts a rotation angle of a longitudinal direction and a rotation angle of a lateral direction of said surveying instrument main body into a vertical angle and a horizontal angle based on a detection result of said attitude detector.