1. A computer apparatus operable to carry out a data processing method to position a set of anatomical landmarks in a three-dimensional image data set of a part or all of a patient, comprising: a. providing a trained supervised machine learning algorithm which has been trained to place each of the set of anatomical landmarks; b. applying the supervised machine learning algorithm to place the set of anatomical landmarks relative to the data set; c. providing a trained point distribution model, including a mean shape and a covariance matrix, wherein the mean shape represents locations of the set of landmarks in a variety of patients; and d. applying the point distribution model to the set of landmarks with the locations output from the supervised machine learning algorithm by: (i) removing any landmarks whose locations have an uncertainty above a threshold with reference to the mean shape and covariance matrix; followed by: (ii) an optimisation of the locations of the remaining landmarks by maximising joint likelihood that a new shape, derived from linear combinations of eigenvectors of the covariance matrix, is plausible.