A method for determining the position of a mobile X-ray detector in an X-ray system , wherein the X-ray system is provided with a 3D camera , the method comprising: acquiring a digital 3D image of the mobile X-ray detector using the 3D camera , wherein the mobile X-ray detector has a X-ray receiving portion on a planar surface and a plurality of passive markers provided on the planar surface having the X-ray receiving portion; detecting the plurality of passive markers and the markers' pattern in the digital 3D image, wherein the pattern of the markers' defines the plane of the mobile X-ray detector having the X-ray receiving portion; estimating the plane of the mobile X-ray detector's X-ray receiving portion; estimating 6 DOF pose of the mobile X-ray detector , wherein the 6 DOF pose defines the position and orientation of the mobile X-ray detector in the 3D camera's coordinate system; and transforming the 6 DOF pose of the mobile X-ray detector in the 3D camera's coordinate system into the corresponding position and orientation in the X-ray base coordinate system, wherein the mobile X-ray detector has four corners and wherein the plurality of passive markers are provided in a specific corner pattern at each of the four corners designating the particular corner, wherein detecting the plurality of passive markers and the marker's pattern in the digital 3D image comprises determining the specific corner patterns, and determining the mobile X-ray detector's orientation, wherein the plurality of passive markers comprise radial corner markers for marking each of the four corners of the mobile X-ray detector and a plurality of smaller point markers for the identification and validation of the radial corner markers. acquiring a digital 3D image of the mobile X-ray detector using the 3D camera , wherein the mobile X-ray detector has a X-ray receiving portion on a planar surface and a plurality of passive markers provided on the planar surface having the X-ray receiving portion; detecting the plurality of passive markers and the markers' pattern in the digital 3D image, wherein the pattern of the markers' defines the plane of the mobile X-ray detector having the X-ray receiving portion; estimating the plane of the mobile X-ray detector's X-ray receiving portion; estimating 6 DOF pose of the mobile X-ray detector , wherein the 6 DOF pose defines the position and orientation of the mobile X-ray detector in the 3D camera's coordinate system; and transforming the 6 DOF pose of the mobile X-ray detector in the 3D camera's coordinate system into the corresponding position and orientation in the X-ray base coordinate system, wherein the mobile X-ray detector has four corners and wherein the plurality of passive markers are provided in a specific corner pattern at each of the four corners designating the particular corner, wherein detecting the plurality of passive markers and the marker's pattern in the digital 3D image comprises determining the specific corner patterns, and determining the mobile X-ray detector's orientation, wherein the plurality of passive markers comprise radial corner markers for marking each of the four corners of the mobile X-ray detector and a plurality of smaller point markers for the identification and validation of the radial corner markers. <EOS>