The common coordinate system could be the coordinate system of the (or of each) virtual camera. However, preferably the common coordinate system is a (fixed) world space coordinate system. When multiple virtual cameras have been defined, preferably a separate transformation is performed for each of the virtual cameras.

When identified features have been matched together using pairs of video camera(s) and/or sensor(s), the common coordinate system may be based on the common coordinate system of a pair of video camera(s) and/or sensor(s). In another embodiment the common coordinate system may be defined based on a display of the system and/or on the walls of the room in which the system is located.

The three-dimensional positions of the features may be transformed in any suitable and desired way. When a point cloud has been formed for a (identified, matched) feature, in one embodiment, preferably the positions in the point cloud are transformed (e.g. moved, rotated and/or scaled) into the common coordinate system. When a plurality of point clouds have been formed (e.g. for multiple identified features), preferably each point cloud is transformed into the common coordinate system. This helps to transform all the determined positions into a single, unified coordinate system. When a single virtual camera has been defined, preferably all the point clouds that have been defined are transformed into the common coordinate system of that virtual camera.