This relates to a system for facilitating spatial positioning including a work space or work site, such as for example a construction site or elsewhere. For example, when the interior of a building is being finished, there is a need to determine the location of various interior features, such as the proper location of walls, windows, and doors. There are a large number of electrical, plumbing, and HVAC components that must be properly sited. Further, beams, joists, ceilings, tiles, shelves, cabinets, and other similar components that must be accurately positioned. After the construction of the interior of the building begins, positioning of various components must be accomplished quickly and with some precision with respect to the surrounding walls, ceilings and floors as they are roughed in. Typically, it has required a significant amount of labor to lay out construction points at a construction site. Teams of workers have been needed to measure and mark various locations. It will be appreciated that this process has been subject to errors, both from measurement mistakes and from accumulated errors which compound as measurements are made from one intermediate point to another. A number of tools have been developed to facilitate this process, although many of these tools are somewhat complicated to use, and require careful attention to achieve the desired accuracy.
Ranging radios offer an excellent alternative to GPS receivers for positioning applications where GPS reception is not available, such as inside a building, or where use of GPS receivers is not reliable. For example, GPS receivers require line-of-sight access to multiple satellites in order to function properly. This may not be possible in some operational settings, such as when work is being performed indoors, underground, or in cluttered environments.
Ranging radios, operating at ultra wideband (UWB) frequencies, provide very accurate measurement of distances between the radios, using time-of-flight analysis. When ranging is accomplished from multiple fixed position radios to a target radio, the relative, three-dimensional position of the target radio is accomplished through trilateration. To perform a range measurement, an originating ranging radio transmits a packet consisting of a synchronization preamble and a header. The header contains the range command with the address of the destination radio that is requested to respond to the packet. The originating radio resets its main counter at the time of this transmission, establishing a local time-zero reference. When the destination ranging radio receives the range request addressed to it, it records the time of receipt, and replies with its own packet, including the time of receipt and the time of the responding transmission in the header. The originating radio receives the ranging packet back from the destination radio, records its time of receipt and latches its main counter. The range value is then calculated and recorded, utilizing the time information to compensate for the differences in the timing clocks at the two radios.
It is desirable to provide an improved system using ranging radios to determine various positions at a work site. A difficulty arises, however, in that a ranging radio may not operate properly throughout a work site, especially if positioned close to a metal surface or beam, or completely or partially shielded from the fixed, reference ranging radios. Further, it is sometimes desirable to be able to determine the position of a point that is not easily accessible.