Surface shape measurement apparatus

An apparatus for measuring a shape of a surface to be measured, the apparatus comprising:

• a measurement head that measures at least one of a distance between a reference point and the surface or a direction of a normal from the surface to the reference point by emitting light that passes through the reference point from the measurement head, and detects test light that is reflected from the surface and returning to the measurement head through the reference point;
• a scanning mechanism that scans the measurement head to move the reference point;
• and
• a processor that:
• calculates the shape of the surface based on a measurement result obtained with the measurement head and coordinates of the reference point;
• calibrates the coordinates of the reference point using a measurement result obtained by measuring a first surface while scanning the measurement head along a scanning path;
• and
• calculates a shape of a second surface, which is different from the first surface, based on a measurement result obtained by measuring the second surface while scanning the measurement head along the same scanning path used for measuring the first surface, and the calibrated coordinates of the reference point.