Radio positioning systems, such as the Global Positioning System (GPS) and others, use radio frequency (RF) signals broadcast from or received at known locations to determine a geographical position of a target object. Great accuracy may be achieved when the RF signals allow a controller which resolves position to gather a sufficient quantity of data. GPS receivers need to receive RF signals from at least three satellites to be able to resolve a position in two dimensions, and accuracy increases as more RF signals are received over longer periods of time.
Unfortunately, radio positioning receivers cannot always receive the needed number of RF signals. For example, when positioning systems are located on vehicles traveling in urban areas, nearby buildings, tunnels, and other obstructions, the various RF signals can be blocked from time to time and prevent the receiver from determining a current position. Consequently, a location system which relies solely upon radio positioning system techniques may be unable to track or continuously provide information describing current positions.
Inertial systems may also be used to determine position. Heading change data may be detected by monitoring a constant inertia device, such as a gyroscope. A controller which resolves position may continuously monitor this heading change data along with speed data and combine these data with other data describing an initial position to track or continuously provide information describing current positions.
Inertial systems can provide current position information when radio positioning systems cannot because inertial systems do not rely upon RF signals which may be blocked by nearby obstructions. Unfortunately, the constant inertia devices, such as gyroscopes and the like, upon which inertial systems rely are error prone. Thus, inertial system position results often become significantly inaccurate.
Constant inertia devices must be manufactured in accordance with exacting processes in order to have a positioning system which approaches a usable degree of accuracy. Mechanical gyroscopes are desirable constant inertia devices to use in vehicles due to their relative insensitivity to temperature changes and their ability to withstand constant minor vibration. However, startup kick, internal friction, and inconsistent road conditions, such as corners, hills, and the like, cause errors which have a tendency to accumulate so that over time unsatisfactory worst case errors are likely to result.