A method of generating model data representative of a model in a three-dimensional space of an object from input signals representative of a set of images of the object taken from a plurality of respective camera positions includes the steps of displaying a model image derived from the model data and having a plurality of primitives for viewing by a user, receiving at least one primitive selection signal responsive to user actuation of an input whereby each primitive selection signal identifies a respective selected primitive of the model, and defining a plurality of virtual cameras in the three dimensional space having positions and look directions relative to the model which correspond substantially to those of the respective actual cameras relative to the object. Additional steps include evaluating which of the virtual cameras is an optimum virtual camera for generating a view of the selected primitives, identifying from the camera images a first camera image of the plurality of camera images taken from a camera position corresponding to that of the optimum virtual camera, and determining from the camera images a second camera image as being suitable for matching features in the first camera image and displaying the second camera image for comparison by the user with the first camera image.