Patent ID: 7330035

Claim:
A method for determining the shape of an unknown object placed in an electrostatic sensing region extending from sensor apparatus comprising a plurality of electrostatic receiving means and at least one electrostatic transmission means, the method comprising: measuring the change in charge induced by said unknown object on each receiving means and storing said charge measurements as a first charge image dataset C f , retrieving a predetermined shape dataset representing point co-ordinates which define said predetermined shape, determining for the first charge image dataset C f a charge distribution dataset q′ representing the charge distribution required on the predetermined shape to substantially result in the measured charge image C f , calculating the electrostatic potential distribution in the sensing region corresponding to said charge distribution dataset q′, generating a new shape dataset having co-ordinates corresponding to points in the sensing region where the electrostatic potential distribution is close to zero, and determining the new shape dataset as representing the shape of the unknown object in the sensing region by comparing the difference between the new shape dataset and the predetermined shape dataset against a predetermined threshold.