Method for determining coordinate system for device under measurement, and coordinate measuring apparatus

A coordinate measuring apparatus for moving an axis and for performing measurement according to a part program, comprising a unit for determining a coordinate system for a device under measurement, in which the direction and position of the coordinate system are determined for the device under measurement according to the position of a feature point obtained by measuring a feature portion of the device under measurement, the relationships of axes in the coordinate system selected in advance being known,

• the unit for determining the coordinate system for the device under measurement comprising:
• a preliminary measurement unit for scanning first measurement areas which include two or more feature portions of the device under measurement with the use of a detector of the coordinate measuring apparatus to obtain position coordinate information and for scanning a second measurement area which includes one or more feature portions that are not on a straight line connecting the first measurement areas, with the use of the detector of the coordinate measuring apparatus, to obtain position coordinate information;
• a feature-point detector for obtaining the position of a feature point in each of the measurement areas according to a result of measurement obtained by the preliminary measurement unit;
• a reference-line determination unit for obtaining a first reference line according to the position of each feature point in the first measurement areas, obtained by the feature-point detector, and for obtaining a second reference line perpendicular to the first reference line and passing through a feature point located in the second measurement area, obtained by the feature-point detector;
• an origin-setting unit for positioning the origin of the coordinate system for the device under measurement according to the position of the intersection of the first reference line and the second reference line obtained by the reference-line determination unit;
• and
• an axis setting unit for determining the directions of axes of the coordinate system for the device under measurement according to the directions of the reference lines obtained by the reference-line determination unit.