Data processing: vehicles – navigation – and relative location – Navigation – Employing position determining equipment
Reexamination Certificate
2001-04-23
2004-11-30
Black, Thomas G. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Navigation
Employing position determining equipment
C701S213000, C701S200000, C340S944000, C073S17800T
Reexamination Certificate
active
06826477
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the field of pedestrian navigation, based at least partially on a so-called “dead reckoning” (DR) approach, in which the evolving position of a pedestrian is determined from within his or her frame of reference. In other words, navigation by DR does not rely on means which use external positional references, such as GPS (global positioning by satellite), rangefinders, etc. It can however make use of the Earth's magnetic field to determine a compass bearing. Navigation by dead reckoning is required when external position references are not available or exploitable. For instance, GPS data cannot reach a pedestrian in surroundings at least partially hidden from elevational lines of sight: buildings, shadowed zones, dense forests, etc. or in case of jamming. GPS data can be used to complement dead reckoning data and also to establish initial calibration and parameterization.
2. Prior Art
Pedestrian navigation by DR is generally based on the detection of body movements during walking. A classical pedometer is one example based on such an approach, where a harmonic motion of a limb is used to count steps. The step count can then be multiplied by a computed stride length to yield an approximate estimate of a total traveled distance. However, a simple pedometer cannot indicate the pedestrian's net displacement in a random walk situation, as the direction of motion is not detected.
More sophisticated pedestrian DR navigation systems aim to estimate walking speed and direction in a combined manner to provide an indication of a net displacement from a known reference point. They also take into account the fact that the stride length varies with walking speed, and cannot be used as a constant factor, as in the case of a simple pedometer.
An example of such a system is disclosed in patent document U.S. Pat. No. 5,583,776 to Levi and Judd. Here, an accelerometer is used to provide acceleration data indicative of footsteps. Specifically, the accelerometer is set to measure a periodic variation in the vertical direction (i.e. in the head-foot alignment). A waveform analysis algorithm based on Fourier analysis is used to detect peaks in the vertical acceleration, these establishing the step frequency. The distance traveled is then derived on the basis of an initial calibration phase, in which a correspondence is established between the pedestrian's walking speed and the fundamental frequency of the vertical acceleration peaks in the frequency spectrum. North and East accumulators are used to track the evolution in direction with the distance traveled.
The vertical acceleration is produced by foot impacts with the ground. This means that the frequency spectrum from the accelerometer varies not only from one person to another, but also on ground conditions. The latter thus constitute an additional variable parameter that must be accommodated by the algorithm. Limits are quickly reached, however, and reliable navigation cannot be expected when the pedestrian is on soft or uneven ground (e.g. muddy fields, gravel, rubble, etc.). Under such conditions, steps can be missed out or over-counted, giving rise to accumulated errors quickly rising to unacceptable levels.
Reliance on vertical acceleration can also lead to false step detection when the pedestrian is jumping on the spot.
Moreover, vertical acceleration data alone does not provide a distinction between normal forward motion steps and backward steps. In other words, it cannot resolve forward/backward motion ambiguity in the pedestrian's step directions. Similarly, vertical acceleration data alone cannot serve to detect side stepping motion, let alone distinguish between left and right side steps. This can be an important drawback for pedestrians such as infantrymen, firefighters, sportsmen, people walking through crowds, cluttered environments, etc. who may be expected to make backward and side movements.
Moreover, vertical acceleration data does not provide a means for identifying steps when climbing up or down stairs in the state of the art.
Finally, useful vertical acceleration data is clearly absent when the pedestrian is effecting a crawling movement.
SUMMARY OF THE INVENTION WITH OBJECTS
It is an object of the present invention to provide a means of pedestrian navigation by dead reckoning (DR), which does not suffer the drawbacks of prior art approaches based on vertical acceleration measurements as the sole source of acceleration data.
The invention thus proposes a new approach to pedestrian navigation which either does not make use of vertical acceleration data, or else uses vertical acceleration, but in conjunction with non-vertical acceleration data, the former complementing the latter.
It is also an object of the invention to provide a compact and highly accurate dead reckoning mode pedestrian navigation apparatus by making use of standard miniaturized inertial navigation system (INS) modules as a source of accelerometric signals. In accordance with this aspect of the invention, one or more signal outputs of an INS module (typically corresponding to three orthogonal axes) is/are analyzed for peak detection, as opposed to being integrated in time in the case of a normal INS application for vehicle navigation. This way of exploiting an INS module output is advantageous from the point of view of miniaturization, economics, accuracy and reliability. It also makes it possible to exploit other sensing devices contained in commercially available INS modules, such as gyroscopes or a digital magnetic compass, temperature or pressure sensors, processor, etc. for realizing the pedestrian navigation apparatus according to the invention. When such an INS module is thus implemented in accordance with the invention, it shall be referred to as a “pedestrian navigation system” (PNS) module.
According to a first aspect, the invention proposes method of determining a displacement of a pedestrian by detecting accelerations of the pedestrian, the method comprising the steps of:
detecting accelerations along a direction which is substantially non-vertical,
determining at least one characteristic feature of the detected accelerations correlated with a displacement step motion, and
determining the displacement on the basis of the determined characteristic feature(s).
The term vertical refers to the direction given by a plumb line, following the usual definition.
Preferably, as will appear further, the accelerations are detected along a direction which is substantially perpendicular to the vertical direction.
The characteristic determination step may comprise the sub-steps of:
detecting a repetition of a the characteristic feature in the accelerations,
measuring a time interval separating a currently detected and a previously detected the characteristic feature, and
determining whether the time interval falls within at least one of an upper and a lower limit,
wherein the displacement determining step comprises the step of considering the currently detected characteristic feature as corresponding to a displacement step if the time interval falls within the limit(s).
the characteristic feature can be a maximum acceleration value or a minimum acceleration value in a determined group of detected acceleration values acquired in a time window.
The acceleration is preferably detected along an antero-posterior (forward-backward) direction of the pedestrian and, depending on the algorithm used, possibly also along a lateral (left-right) direction of the pedestrian.
The step characteristic feature determining step preferably involves determining a peak acceleration from the detected accelerations and correlating the peak with a motion of the body corresponding to a displacement.
The method may further comprise the step of detecting whether the pedestrian is moving or not, the determining step comprising:
acquiring acceleration values during a time interval,
calculating a variance in the acquired acceleration values, comparing the variance to a determined thresh
Gabaglio Vincent
Ladetto Quentin
Van Seeters Josephus
Black Thomas G.
Ecole Polytechnique Federale de Lausanne (EPFL)
Hernandez Olga
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