1. A method of determining extrinsic calibration parameters for at least one sensor mounted on transportable apparatus, the method including: receiving data representing pose history of the transportable apparatus; receiving sensor data from at least one sensor mounted on transportable apparatus; generating at least one point cloud datum using the sensor data received from the at least one sensor, each point in a said point cloud having a point covariance derived from the pose history data; maximising a value of a quality function for the at least one point cloud; and using the maximised quality function to determine extrinsic calibration parameters for the at least one sensor.