Patent ID: 7940260

Claim:
A method comprising: acquiring three-dimensional surface data from a subject as a sequence of three-dimensional images at a frame rate, each one of the sequence of three-dimensional images fitted to at least one previous one of the sequence of three-dimensional images; acquiring an image set for a next three-dimensional image at the frame rate; when the image set can be converted into the next three-dimensional image and the next three-dimensional image can be fitted to the three-dimensional surface data, superimposing the three-dimensional surface data and the next three-dimensional image onto a two-dimensional image of the subject in a display; and when the image set cannot be converted into the next three-dimensional image or the next three-dimensional image cannot be fitted to the three-dimensional surface data, entering a recover mode comprising the steps of: superimposing a current two-dimensional image of the subject onto a previous two-dimensional image of the subject in the display at the frame rate, the previous two-dimensional image representing a view of the subject from a position from which one of the sequence of three-dimensional images was acquired, and the current two-dimensional image representing a view of the subject from a position from which the image set was acquired; acquiring at least one subsequent three-dimensional image; and test fitting the at least one subsequent three-dimensional image to one or more of the sequence of three-dimensional images.