SURVEYING POLE AND SECONDARY SENSOR UNIT HAVING TOROIDAL FORM

A surveying pole and to a secondary sensor unit which is attachable to the surveying pole. A reflector and/or GNSS receiver attachable to the surveying pole can be attached independently of whether or not the secondary sensor unit is attached to the surveying pole. A distance between the reflector and/or GNSS receiver and a pole tip is also independent of whether or not the secondary sensor unit is attached to the surveying pole. A distance between an attached reflector and/or GNSS receiver and the attached secondary sensor unit is also known and fixed. A method and computer program product for numerically correcting distance measurement errors due to reflector orientation and position with respect to a primary sensor, in particular a tachymeter.