Spatially locating radio tags for on demand systems

A method of spatially locating RFID tags, said method comprising:

• transmitting a request signal from at least one of a plurality of RFID readers;
• receiving an RFID tag response signal at said plurality of RFID readers;
• determining a plurality of time-of-flight factors;
• determining a plurality of correction factors;
• adjusting said plurality of time-of-flight factors by applying said plurality of correction factors to said plurality of time-of-flight factors;
• determining based in part on said plurality of time-of-flight factors a plurality of distances between each of said plurality of RFID readers and said RFID tag;
• determining based in part on said plurality of distances the spatial location of said RFID tag;
• detecting disagreements between said plurality of readers as to the presumed spatial location of said RFID tag resultant from reflected signal paths;
• and
• adjusting for spurious distances resultant from reflected signal paths by using mathematically modeled and saved RFID tag spatial location data near the determined said RFID tag spatial location.