Apparatus, method and program for spatial position measurement

A spatial position measurement apparatus, comprising:

• a transmission unit configured to transmit an ultrasonic wave accompanying with a transmission source identifiable from a group of three or more transmission sources planarly provided on a first object,
• a detection unit configured to detect the ultrasonic wave received by a group of two or more reception sensors linearly provided on a second object, and
• circuitry configured to
• calculate distances between each of the transmission sources and the reception sensors based on propagation time of the ultrasonic wave,
• calculate, in a coordinate system where positional coordinates of one group out of the group of the transmission sources and the group of the reception sensors are fixed, positional coordinates of another group based on the distances,
• derive an equation of a plane including the positional coordinates of the group of the transmission sources and a linear equation including the positional coordinates of the group of the reception sensors;
• and
• a relative angle calculation unit configured to calculate a relative angle between the first object and the second object, the relative angle calculated as a crossed axes angle between a normal vector of the equation of the plane and a linear direction vector of the linear equation.