Angle detection system

An angle detection system comprising:

• a target unit including a reflection target and an encoder pattern showing an angle in a circumferential direction around a central axis of the target unit;
• and
• a surveying instrument including a survey unit configured to perform a distance measurement and angle measurement to the reflection target, an encoder pattern reading unit configured to read a bit pattern by acquiring an image including the encoder pattern, cutting out a region of the encoder pattern from the image, and reading pixel rows, a display unit, and an arithmetic control unit, wherein
• the encoder pattern reading unit includes at least one imaging unit changeable in focal length, and
• the arithmetic control unit includes
• a distance and angle operation unit configured to calculate a distance and an angle to the reflection target based on the results of distance and angle measurement,
• an imaging magnification setting unit configured to set an imaging magnification of the imaging unit according to the distance,
• a cutout range adjusting unit enabling setting of a cutout region of the encoder pattern by using the image displayed on the display unit,
• an encoder pattern identification determination unit configured to determine whether or not encoder pattern identification is successful by collating the acquired image of the encoder pattern with a pattern template of an encoder pattern stored in advance in a storage unit, and perform reading again at an increased imaging magnification when the encoder pattern identification fails, and
• a read angle operation unit configured to calculate an encoder pattern read angle θE based on an image of an identified encoder pattern.