1. A method of tracking parameters of an entity of a first type comprising: receiving, from a time of flight camera, first raw image data depicting the entity; accessing a stored 3D model of the first type of entity, the 3D model having tracked model parameters; selecting candidate values for the tracked model parameters, wherein the selection comprises: selecting a first set and second set of candidate values; rendering, from the 3D model using the first set and second set of candidate values, respective second and third simulated raw time of flight image data, the second and third simulated raw time of flight image data including historical data that is perturbed to generate a first and second predicted pose corresponding to the 3D model with the first and second set of candidate values respectively; comparing the second simulated raw time of flight image data and at least part of the received first raw image data and the third simulated raw time of flight image data and the at least part of the received first raw image data; and determining that the second simulated raw time of flight image data corresponding to the 3D model with the first set of candidate values used to generate the first predicted pose is closer to the first raw image data than the third simulated raw time of flight image data corresponding to the 3D model with the second set of candidate values used to generate the second predicted pose; and in response to determining that the second simulated raw time of flight image data is closer to the first raw image data, selecting the first predicted pose as an estimated pose of the entity; and outputting the estimated pose of the entity.