The disclosure relates to a method of calibrating a camera system to a radiotherapy treatment room, and utilizing said calibrated camera system for surface modelling and tracking of a patient in said radiotherapy treatment room, wherein the camera system comprises a plurality of cameras arranged on a plurality of camera rigs. The method utilizes a calibration sheet with a known pattern to calibrate the cameras in view of determining positions of centers of circles of the calibration sheet. From the determined positions of the centers of the circles a relative orientation of the cameras on each of the camera rigs is determined and the camera positions in relation to the focusing point of the treatment room is determined. The method further focuses on creating transformations for matching points in obtained images from the plurality of cameras, wherein the transformations are utilized to generate a surface model of a patient lying on the couch.
