A system for taking inventory of objects and estimating the position of objects comprising RFID tags, the system comprising: at least one RFID reader moveable in a given space and suitable for detecting RFID tags in the given space; means for estimating the position and/or orientation of the RFID reader in the given space, comprising at least means external to the RFID reader for measuring the position and/or orientation of the RFID reader, wherein all or part of the means external to the RFID reader are not moved together with the RFID reader through the given space and the means external to the RFID reader are arranged within the given space; means for estimating the position of the RFID tags with respect to the RFID reader; the system being adapted to estimate the position of the objects in the given space using the estimated position of the RFID tags with respect to the RFID reader and the estimated position and/or orientation of the RFID reader in the given space; and the system being adapted to take inventory of the objects using at least information on detected RFID tags; wherein the means for estimating the position of the RFID tags with respect to the RFID reader are adapted to estimate the position of the RFID tags with respect to the RFID reader using at least one of: a geometric model of the RFID reader, an electromagnetic radiation model of the RFID reader, a measured model of the RFID reader; wherein estimating the position of the RFID tags with respect to the RFID reader is characterized by using a point cloud covering a volume in which the RFID tags could be and using a best fit model to determine the most likely position of the RFID tags within the point cloud. at least one RFID reader moveable in a given space and suitable for detecting RFID tags in the given space; means for estimating the position and/or orientation of the RFID reader in the given space, comprising at least means external to the RFID reader for measuring the position and/or orientation of the RFID reader, wherein all or part of the means external to the RFID reader are not moved together with the RFID reader through the given space and the means external to the RFID reader are arranged within the given space; means for estimating the position of the RFID tags with respect to the RFID reader; the system being adapted to estimate the position of the objects in the given space using the estimated position of the RFID tags with respect to the RFID reader and the estimated position and/or orientation of the RFID reader in the given space; and the system being adapted to take inventory of the objects using at least information on detected RFID tags; wherein the means for estimating the position of the RFID tags with respect to the RFID reader are adapted to estimate the position of the RFID tags with respect to the RFID reader using at least one of: a geometric model of the RFID reader, an electromagnetic radiation model of the RFID reader, a measured model of the RFID reader; wherein estimating the position of the RFID tags with respect to the RFID reader is characterized by using a point cloud covering a volume in which the RFID tags could be and using a best fit model to determine the most likely position of the RFID tags within the point cloud.