Method for monitoring the location of monitored objects

A method for monitoring the location of monitored objects within a monitored area, comprising the steps of:

• positioning signpost units within the monitored area, each signpost unit being positioned at the intersection of a first coordinate grid line and a second coordinate grid line with the first coordinate grid lines being spaced generally in a first direction and extending generally in a second direction and with the second coordinate grid lines being spaced generally in the second direction and extending generally in the first direction, the first coordinate grid lines being assigned numbers sequentially increasing in the first direction and the second coordinate grid lines being assigned numbers sequentially increasing in the second direction, each signpost unit having a signpost code encoded therein uniquely identifying the signpost unit and having a first portion corresponding to the number assigned to the first coordinate grid line and a second portion corresponding to the number assigned to the second coordinate grid line of the intersecting first and second coordinate grid lines defining the position of the signpost unit;
• transmitting the signpost codes via the signpost units;
• receiving the signpost codes at the monitored objects, each received signpost code being a new signpost code and the signpost code received prior to the new signpost code being the last signpost code;
• and
• determining at the monitored object the location of the monitored object within the monitored area, comprising the steps of:
• selecting one of the new signpost code and the last received signpost code as a reference signpost code;
• comparing the first portion of the new signpost code with the first portion of the last signpost code and comparing the second portion of the new signpost code with the second portion of the last signpost code;
• determining the monitored object to be located at the signpost unit identified via the reference signpost code in response to a comparison indicating the first and the last portions of the new signpost code and the last received signpost code are the same;
• and
• determining the direction of the monitored object from the signpost unit identified via the reference signpost code in response to a comparison indicating a difference between any one of the comparisons of the first and last portions of the new signpost code and the last received signpost code.