Patent ID: 7542872

Claim:
A form measuring instrument for measuring a form of a surface of an object to be measured using a contact to follow the surface, the instrument comprising: a pseudo-measurement point acquirer operative to acquire positional coordinates of the reference point of the contact as pseudo-measurement points when the contact touches the object at a plurality of locations; a normal vector generator operative to estimate a surface or line along the pseudo-measurement points from the pseudo-measurement points to calculate normal vectors extending from the pseudo-measurement points to the surface or line; a contact model locator operative to locate contact models which are located in a pseudo space generated by computing and that specify the surface form of the contact so as to coincide the pseudo-measurement points with reference points of the contact models and so as to coincide attitudes of the contact on measurement with attitudes of the contact models; and a measurement point calculator operative to calculate cross points as measurement points, at which the normal vectors cross the surfaces of the located contact models.