A method of determining a 3D position of an object in space, the method comprising the steps of - attaching an optical-tracking marker to the object, said optical-tracking marker comprising an inner marker body having an elliptical shape and a geometric center, said inner marker body being filled with color spectrum points radially spread with respect to the geometric center, wherein a color value of each spectrum point of the inner marker body is calculated as a function of an angle defined between a horizontal line crossing the central point and a further line crossing the central point as well as the respective spectrum point, - capturing a first digital image of said optical-tracking marker using a first camera and capturing a further digital image of said optical-tracking marker using a further camera, - detecting, within the first and further digital images, edges of the optical-tracking marker, - determining a 2D location of the optical-tracking marker in each of the first digital image and the further digital image, and - determining a 3D location of the optical-tracking marker in space based on the 2D locations in each of the first digital image and the further digital image, characterized in that the color values of the respective spectrum points vary in accordance with a sinusoidal pattern along an elliptical path around the center point, and the method comprising the further steps of - detecting blobs within a respective set of detected edges in the first and further digital images, - detecting ellipses within a respective set of detected blobs, and - analyzing the sinusoidal pattern within each of the detected ellipses, wherein the step of determining the 2D location of the optical-tracking marker in each of the first digital image and the further digital image is based on the analysis of the sinusoidal pattern. - attaching an optical-tracking marker to the object, said optical-tracking marker comprising an inner marker body having an elliptical shape and a geometric center, said inner marker body being filled with color spectrum points radially spread with respect to the geometric center, wherein a color value of each spectrum point of the inner marker body is calculated as a function of an angle defined between a horizontal line crossing the central point and a further line crossing the central point as well as the respective spectrum point, - capturing a first digital image of said optical-tracking marker using a first camera and capturing a further digital image of said optical-tracking marker using a further camera, - detecting, within the first and further digital images, edges of the optical-tracking marker, - determining a 2D location of the optical-tracking marker in each of the first digital image and the further digital image, and - determining a 3D location of the optical-tracking marker in space based on the 2D locations in each of the first digital image and the further digital image, - detecting blobs within a respective set of detected edges in the first and further digital images, - detecting ellipses within a respective set of detected blobs, and - analyzing the sinusoidal pattern within each of the detected ellipses, <EOS>