Offset calculation device and azimuth sensor therewith

An azimuth sensor comprising:

• a magnetism detection device configured to generate three-axis or two-axis magnetism detection data;
• an offset calculation device configured to calculate an offset for the magnetism detection data;
• an offset correction device configured to correct the offset for the magnetism detection data;
• and
• an azimuth calculation device configured to generate azimuth data from corrected magnetism detection data,
• wherein the offset calculation device is configured to perform, as offset calculation processing for processing the three-axis or two-axis magnetism detection data sequentially acquired as data points in a three-axis or two-axis coordinate system, the following operations sequentially:
• translate N data points (where N≥2) evenly such that one reference data point arbitrarily selected from the N data points coincides with an origin and translating also (N−1) data points other than the reference data point by a same amount of translation as the reference data point, thereby to derive (N−1) virtual data points except for the reference data point,
• calculate a virtual offset point that minimizes a sum of distances from a curved surface passing through the origin to the (N−1) virtual data points respectively, and
• calculate offset values for the magnetism detection data by translating the virtual offset point inversely to a previous translation,
• wherein for the (N−1) virtual data points are represented by (Hxi′, Hyi′, Hzi′) (where i=1 to N−1), and the virtual offset point represented by (Hx0′, Hy0′, Hz0′), the offset calculation device is configured to calculate the virtual offset point such as to minimize a function H1, where
• H1=Σi(Hxi′2+Hyi′2+Hzi′2−2Hxi′·Hx0′−2Hyi′·Hy0′−2Hzi′·Hz0′)2.