A method for calibrating a projection device, in particular a hand-held projection device, in a navigational environment for medical purposes, comprising the steps of: - providing a projection device comprising a reference array that is adapted to be tracked by means of a tracking system, and a detection device having a reference array that is adapted to be tracked by means of a tracking system, the detection device being configured to detect light emitted by the projection device; - determining the spatial position of the detection device by means of the tracking system; - using the projection device to project a projection towards the detection device, wherein the projection comprises, at a known position in the projection, an area configured to stimulate the detection device; - determining the spatial position of the projection device by means of the tracking system when the area stimulates the detection device, wherein determining the spatial position of the projection device is triggered automatically by means of the detection device sending a trigger signal when the area of the projection stimulates the detection device, wherein the step of determining the spatial position of the projection device is performed several times, and wherein the spatial position of the projection device and/or the position of the area within the projection is changed between the several determination steps; - determining, based on the known positions of the area in the projection, the determined spatial positions of the projection device, and the determined spatial position of the detection device, the spatial relationship between the projection generated by the projection device and the reference array of the projection device. - providing a projection device comprising a reference array that is adapted to be tracked by means of a tracking system, and a detection device having a reference array that is adapted to be tracked by means of a tracking system, the detection device being configured to detect light emitted by the projection device; - determining the spatial position of the detection device by means of the tracking system; - using the projection device to project a projection towards the detection device, wherein the projection comprises, at a known position in the projection, an area configured to stimulate the detection device; - determining the spatial position of the projection device by means of the tracking system when the area stimulates the detection device, wherein determining the spatial position of the projection device is triggered automatically by means of the detection device sending a trigger signal when the area of the projection stimulates the detection device, wherein the step of determining the spatial position of the projection device is performed several times, and wherein the spatial position of the projection device and/or the position of the area within the projection is changed between the several determination steps; - determining, based on the known positions of the area in the projection, the determined spatial positions of the projection device, and the determined spatial position of the detection device, the spatial relationship between the projection generated by the projection device and the reference array of the projection device.