Pedestrian navigation method and apparatus operative in a dead reckoning mode

• US 20030018430A1
• Filed: 04/23/2001
• Published: 01/23/2003
• Est. Priority Date: 04/23/2001
• Status: Active Grant

• Current Assignee: Ecole polytechnique fãdãrale de lausanne epfl (Schweizerische Eidgenossenschaft)
• Original Assignee: Ecole polytechnique fãdãrale de lausanne epfl (Schweizerische Eidgenossenschaft)
• Inventors: Gabaglio, Vincent, Ladetto, Quentin, Van Seeters, Josephus
• Granted Patent: US 6,826,477 B2
• Time in Patent Office: Days
• US Class Current: 701/217
• CPC Class Codes: G01C 21/166 Mechanical, construction or arrangement details of inertial navigation systems
• CPC Class Codes: G01C 21/206 specially adapted for indoor navigation
• CPC Class Codes: G01C 22/006 Pedometers
• CPC Class Codes: G06F 2218/00 Aspects of pattern recognition specially adapted for signal processing
• CPC Class Codes: G06V 40/25 Recognition of walking or running movements, e.g. gait recognition

Abstract

A displacement of a pedestrian is determined from his or her accelerations by detecting accelerations which is substantially non vertical, determining a characteristic feature in the detected accelerations correlated with a step frequency, determining the displacement on the basis of said determined characteristic.

The acceleration data can be submitted to waveform analysis to determine an actualized time interval of an occurring feature, such a maximum values, from which it is determined whether the actualized time period falls within determined limit values. The currently detected characteristic feature is then determined as corresponding to a displacement step if the actualized time period falls within said determined limit value.

By using non-vertical acceleration measurements, the invention can make it possible to distinguish between forward, backward, left and right stepping movements and take these into account for the navigation.

Claims

1. A method of determining a displacement of a pedestrian by detecting accelerations of said pedestrian, said method comprising the steps of:

detecting accelerations along a direction which is substantially non-vertical,

determining at least one characteristic feature of said detected accelerations correlated with a displacement step motion, and

determining said displacement on the basis of said determined characteristic feature(s).

2. The method of claim 1, wherein said characteristic determination step comprises the sub-steps of:

detecting a repetition of a said characteristic feature in said accelerations,

measuring a time interval separating a currently detected and a previously detected said characteristic feature, and

determining whether said time interval falls within at least one of an upper and a lower limit,

and wherein said displacement determining step comprises the step of considering said currently detected characteristic feature as corresponding to a displacement step if said time interval falls within said limit(s).

3. The method of claim 2, wherein said characteristic feature is a maximum acceleration value or a minimum acceleration value in a determined group of detected acceleration values acquired in a time window.

4. The method of claim 1, wherein said acceleration is detected along an antero-posterior (forward-backward) direction of said pedestrian.

5. The method of claim 1, wherein said acceleration is detected along a lateral (left-right) direction of said pedestrian.

6. The method of claim 1, wherein said step characteristic feature determining step involves determining a peak acceleration from said detected accelerations and correlating said peak with a motion of the body corresponding to a displacement.

7. The method of claim 1, further comprising the step of detecting whether said pedestrian is moving or not, said determining step comprising:

acquiring acceleration values during a time interval,

calculating a variance in said acquired acceleration values,

comparing said variance to a determined threshold, and

considering that said pedestrian is moving if the variance is superior to said threshold.

8. The method of claim 1, further comprising determining a direction, relative to said pedestrian, of a detected step.

9. The method of claim 1, further comprising a step of distinguishing between whether said pedestrian is making a step in an antero-posterior sense (forward or backward direction) on the one hand, and in a lateral sense (left or right direction) on the other, said distinguishing step comprising:

determining a variance of successive acceleration values over a given time period for both an acceleration in the antero-posterior sense and in the lateral sense,

comparing the variance determined for the antero-posterior acceleration values with the variance determined for the lateral acceleration values,

determining that said pedestrian is making a step in said antero-posterior sense if the variance of said antero-posterior acceleration values exceeds the variance of said lateral acceleration values, and

determining that said pedestrian is making a step in said lateral sense if the variance of said lateral acceleration values exceeds the variance of said antero-posterior acceleration values.

10. The method of claim 1, further comprising a step of distinguishing between forward and backward steps relative to said pedestrian, said distinguishing step comprising:

detecting accelerations along an antero-posterior (forward-backward) direction relative to said pedestrian,

determining a time of occurrence of a current first characteristic value and a previous first characteristic value in the antero-posterior accelerations,

determining whether a time interval separating said current and previous first characteristic values is within determined time limits,

determining a time of occurrence of a second characteristic value in the antero-posterior accelerations occurring within a time range at least sufficiently large to contain said determined time limits, and

discriminating between a forward and a backward step on the basis of the order of occurrence of said current first characteristic value and said second characteristic value.

11. The method of claim 10, wherein said first characteristic value is a maximum value in a group of detected acceleration values, and said second characteristic value is a minimum value of said detected accelerations, and wherein said displacement step is determined as corresponding to a forward displacement step if said minimum value precedes said maximum value, and as corresponding to a backward step if said maximum value precedes said minimum value.

12. The method of claim 1, further comprising a step of distinguishing between left and right displacement steps relative to said pedestrian, said distinguishing step comprising:

detecting accelerations along a lateral (left-right) direction relative to said pedestrian,

determining a time of occurrence of a current first characteristic value and a previous first characteristic value in the lateral accelerations,

determining whether a time interval separating said current and previous first characteristic values is within determined time limits,

determining a time of occurrence of a second characteristic value in the lateral accelerations occurring within a time range at least sufficiently large to contain said determined time limits, and

discriminating between a left and a right step on the basis of the order of occurrence of said current first characteristic value and said second characteristic value.

13. The method of claim 12, wherein said first characteristic value is a maximum value in a group of detected acceleration values, and said second characteristic value is a minimum value of said detected accelerations, and wherein said displacement step is determined as corresponding to a right displacement step if said minimum value precedes said maximum value, and as corresponding to a left displacement step if said maximum value precedes said minimum value.

14. The method of claim 1, wherein said acceleration detecting step further comprises detecting accelerations along said vertical direction.

15. The method of claim 1, wherein said characteristic determination step comprises the sub-steps of:

determining a first time corresponding to an occurrence of a characteristic feature in said accelerations along a direction substantially perpendicular to a vertical direction of said pedestrian,

detecting accelerations along a vertical direction of said pedestrian,

determining a second time corresponding to an occurrence of said characteristic feature in said accelerations along a vertical direction of said pedestrian,

comparing said first and second times, and

using a result of said comparison to confirm the presence of a displacement step.

16. The method of claim 15, wherein said characteristic feature is a maximum acceleration value in a determined group of detected acceleration values.

17. The method of claim 1, wherein a step direction in at least one of an antero-posterior (forward-backward) sense and a lateral (left-right) sense is distinguished using a model adapted to recognize patterns in detected acceleration values that are representative of specific step directions.

18. The method of claim 17, wherein said model is a Hidden Markov Model.

19. The method of claim 1, wherein:

said acceleration detecting step comprises acquiring successive acceleration values,

said characteristic and displacement determination steps comprise the sub-steps of;

determining a current peak acceleration in said successive acceleration values by means of a sliding window,

determining a variance of said successive acceleration values acquired between said current peak and a previous peak acceleration value,

comparing said variance to an adaptive threshold to detect if said pedestrian is walking or not,

determining whether the time interval between two successive peak acceleration values falls within a physiologically possible time interval, and

storing the time of acquisition of said current peak acceleration value as the time of occurrence of a detected foot impact corresponding to a displacement step.

20. The method of claim 1, wherein said displacement determining step involves determining a distance traveled by using at least one first model which yields a pedestrian displacement speed in response to a variance and/or a frequency of occurrence of said characteristic feature in values of said acquired accelerations, and at least a time indicator or a second model which correlates a pedestrian displacement speed obtained by said first model with a step length.

21. The method of claim 20, wherein said first mathematical model correlates displacement speed with said variance in accordance with the following relationships:

2-dimensional relative speed=D*(variance)^E+F*frequency of steps;

displacement speed=2-dimensional displacement speed+V_baro

where D, E and F are numerical coefficients from which D and F can be set equal to 0 or finite values and V_baro is the vertical velocity measured by a barometer, 2-dimensional displacement speed being obtained by multiplying the 2-dimensional relative speed by stature or the leg length according to the model which is chosen and 3-dimensional displacement speed then being computed by adding the vertical displacement V_baro to the 2-dimensional displacement speed.

22. The method of claim 20, wherein said first mathematical model correlates displacement speed with either said variance or a frequency of occurrence of said characteristic feature in accordance with the following relationship:

2-dimensional relative Speed=A*(Frequency or Variance)^B+C,

displacement speed=2-dimensional displacement speed +V_baro

where A, B and C are numerical coefficients and V_baro is the vertical velocity measured by the barometer, the 2-dimensional displacement speed being obtained by multiplying the 2-dimensional relative speed by stature or the leg length according to the model which is chosen and 3-dimensional displacement speed then being computed by adding the vertical displacement V_baro to the 2-dimensional displacement speed.

23. The method of claim 20, wherein said time indicator correspond to a time interval between two successive said characteristic features, whereby:

step length=speed*time between two successive characteristic features

or wherein said second mathematical model correlates step length with displacement speed in accordance with the following relationships;

step length=sl_o+m*displacement speed;

where sl_o is a fraction of the step length which is constant and independent of speed of progression, and m is a slope of a function describing the step length as a function of displacement speed.

24. The method of claim 23, wherein an initial sl_o value is determined with different model for a male or a female pedestrian.

25. The method of claim 20, further comprising the step of updating at least one parameter of said second mathematical model on the basis of external positioning data, such as data from a global positioning by satellite (GPS) system.

26. The method of claim 1, wherein said displacement determining step involves calculating a displacement on foot and/or a displacement speed of said pedestrian.

27. The method of claim 1, further comprising the step of azimuth computation for each step or group of steps effected to determine a position of said pedestrian.

28. The method of claim 27, wherein an azimuth computation is computed for each determined displacement step, said computation comprising the steps of:

distinguishing a direction of a step between forward, backward, left and right displacement steps,

detecting an azimuth from a sensor carried by said pedestrian,

correcting said detected azimuth with an offset angle in accordance with a distinguished of step.

29. The method of claim 27, wherein said azimuth computation is performed from azimuth signals produced by magnetic sensor means.

30. The method of claim 27, wherein said azimuth computation step is performed from azimuth signals produced by magnetic sensor means yielding raw angular data signals, said step comprising a sub step of extracting the cosine and sine components of said raw azimuth data and filtering said cosine and sine components.

31. The method of claim 27, wherein said azimuth computation is performed from azimuth signals produced by a gyroscopic sensor.

32. The method of claim 27, wherein said azimuth computation is performed by magnetic sensor means and by other sensor means not dependent on the North magnetic field, such as gyroscope means, said method further comprising the steps:

comparing azimuth readings from said magnetic and said other sensor means, and

ignoring azimuth readings from said magnetic sensor means if said comparison step reveals a discrepancy between said readings exceeding a limit value, indicative of a significant magnetic disturbance.

33. The method of claim 1, further comprising a step of detecting an about turn in a displacement of said pedestrian, comprising:

detecting a condition in which an azimuth rate of change of said pedestrian exceeds a determined threshold,

determining whether said azimuth rate of change corresponds roughly to a 180°

turn,

in the affirmative, determining whether alignments of trajectories before and after said turn are the same to within a determined discrepancy limit,

in the affirmative, considering that an about turn is effected.

34. The method of claim 33, wherein any step made during a period in which said azimuth rate of change exceeds said determined threshold is not used to calculate a distance of displacement.

35. The method of claim 33, wherein an azimuth is calculated on the basis of an average between said alignments corresponding to a forward and return path.

36. The method of claim 33, wherein said about turn is considered to be effected only on the further condition that a trajectory effected after said azimuth rate of change of said pedestrian exceeding a determined threshold is shorter than the trajectory effected before said azimuth rate of change of said pedestrian exceeds a determined threshold.

37. The method of claim 1, further comprising the step of acquiring barometer data to determine an elevational component in said determined displacement.

38. The method of claim 1, further comprising the step of using means satellite positioning means to correct displacement information obtained through said accelerations.

39. The method of claim 1, wherein said accelerations are detected by acceleration sensor means mounted on the waist of said pedestrian.

40. The method of claim 1, wherein said accelerations are detected by acceleration sensor means mounted on the trunk of said pedestrian.

41. The method of claim 1, wherein said accelerations are detected by using sensors of an inertial navigation system (INS).

42. The method of claim 41, wherein said sensors are housed in a module together with azimuth detection means, said azimuth detection means being one of magnetic sensor means and/or gyroscope means, and being used to acquire azimuth data.

43. The method of claim 1, wherein said accelerations are detected by means of three mutually orthogonal acceleration sensors each delivering an acceleration component of a respective orthogonal axis on a separate channel.

44. The method of claim 1, wherein said accelerations are detected by means of two mutually orthogonal acceleration sensors each delivering an acceleration component operatively aligned along a respective orthogonal axis, the alignment of at least one of said sensors having a component in a non vertical direction when operatively carried by said pedestrian.

45. The method of claim 44, wherein at least one said axis of an accelerometer is inclined with respect to a vertical axis of said pedestrian.

48. The method of claim 47, wherein said INS also has a motion sensor responsive to accelerations along a lateral (left-right) direction of said pedestrian, signals therefrom being submitted to a waveform analysis to determine a left or right displacement effected by said pedestrian.

49. The method of claim 48, wherein said INS also has a motion sensor responsive to accelerations along a vertical direction of said pedestrian, signals therefrom being submitted to a waveform analysis to provide a confirmation of a determination of a displacement step.

50. The method of claim 48, wherein said INS further comprises bearing detection means in the form of magnetometer means or gyroscope means, said means being used to obtain an azimuth of said pedestrian for the determination of said navigation information.

51. The method of claim 47, wherein said INS is in the form of a module carried on the waist of said pedestrian.

52. The method of claim 48, wherein said INS is in the form of a module carried on trunk of said pedestrian.

54. The apparatus of claim 1, wherein said characteristic determining means comprises:

means for detecting a repetition of a said characteristic feature in said accelerations,

means for measuring a time interval separating a currently detected and a previously detected said characteristic feature, and

means for determining whether said time interval falls within at least one of an upper and a lower limit,

and wherein said displacement determining means comprises means for considering said currently detected characteristic feature as corresponding to a displacement step if said time interval falls within said limit(s).

55. The apparatus of claim 54, wherein said characteristic feature is a maximum acceleration value or a minimum acceleration value in a determined group of detected acceleration values acquired in a time window.

46. A method of pedestrian navigation operative in a dead reckoning mode, comprising the steps of:

detecting an evolving signal indicative of accelerations of said pedestrian in the antero-posterior (forward-backward) direction,

analyzing said signals to determine a variation therein conforming to predetermined constraints,

using said variation to establish a displacement step motion and to determine displacement information comprising at least one of a speed and distance of displacement,

determining an azimuth of said pedestrian, and

combining said displacement data with said azimuth to obtain pedestrian navigation information.

47. A method of pedestrian navigation operative in a dead reckoning mode, comprising the steps of:

using an Inertial Navigation System (INS) as a source acceleration signals, said system having a motion detection sensor responsive to accelerations along the antero-posterior (forward-backward) direction of said pedestrian,

submitting signals from said INS to a waveform analysis to determine a step of said pedestrian, and

determining pedestrian navigation information on the basis of said waveform analysis.

53. An apparatus for determining a displacement of a pedestrian by detecting accelerations of said pedestrian, said apparatus comprising:

sensing means for detecting accelerations along a direction which is substantially non-vertical,

characteristic determining means for determining at least one characteristic feature of said detected accelerations correlated with a displacement step motion, and

displacement determining means for determining said displacement on the basis of said determined characteristic feature(s).

56. The apparatus of claim 53, wherein said acceleration is detected along an antero-posterior (forward-backward) direction of said pedestrian.

57. The apparatus of claim 53, wherein said acceleration is detected along a lateral (left-right) direction of said pedestrian.

58. The apparatus of claim 53, wherein said step characteristic feature determining means is operative to detect a peak acceleration from said detected accelerations and to correlate said peak with a motion of the body corresponding to a displacement.

59. The apparatus of claim 53, further comprising motion detecting means for detecting whether said pedestrian is moving or not, said means comprising:

means for acquiring acceleration values during a time interval,

means for calculating a variance in said acquired acceleration values,

means for comparing said variance to a determined threshold, and

means for considering that said pedestrian is moving if the variance is superior to said threshold.

60. The apparatus of claim 53, further comprising direction determining means for determining a direction, relative to said pedestrian, of a detected step.

61. The apparatus of claim 53, further comprising first distinguishing means for distinguishing between whether said pedestrian is making a step in an antero-posterior sense (forward or backward direction) on the one hand, and in a lateral sense (left or right direction) on the other, said first distinguishing means comprising:

means for determining a variance of successive acceleration values over a given time period for both an acceleration in the antero-posterior sense and in the lateral sense,

means for comparing the variance determined for the antero-posterior acceleration values with the variance determined for the lateral acceleration values,

means for determining that said pedestrian is making a step in said antero-posterior sense if the variance of said antero-posterior acceleration values exceeds the variance of said lateral acceleration values, and

means for determining that said pedestrian is making a step in said lateral sense if the variance of said lateral acceleration values exceeds the variance of said antero-posterior acceleration values.

62. The apparatus of claim 53, further comprising second distinguishing means for distinguishing between forward and backward steps relative to said pedestrian, said second distinguishing means comprising:

means for detecting accelerations along an antero-posterior (forward-backward) direction relative to said pedestrian,

means for determining a time of occurrence of a current first characteristic value and a previous first characteristic value in the antero-posterior accelerations,

means for determining whether a time interval separating said current and previous first characteristic values is within determined time limits,

means for determining a time of occurrence of a second characteristic value in the antero-posterior accelerations occurring within a time range at least sufficiently large to contain said determined time limits, and

means for discriminating between a forward and a backward step on the basis of the order of occurrence of said current first characteristic value and said second characteristic value.

63. The apparatus of claim 62, wherein said first characteristic value is a maximum value in a group of detected acceleration values, and said second characteristic value is a minimum value of said detected accelerations, and wherein said displacement step is determined as corresponding to a forward displacement step if said minimum value precedes said maximum value, and as corresponding to a backward step if said maximum value precedes said minimum value.

64. The apparatus of claim 53, further comprising third distinguishing means for distinguishing between left and right displacement steps relative to said pedestrian, said third distinguishing step comprising:

means for detecting accelerations along a lateral (left-right) direction relative to said pedestrian,

means for determining a time of occurrence of a current first characteristic value and a previous first characteristic value in the lateral accelerations,

means for determining whether a time interval separating said current and previous first characteristic values is within determined time limits,

means for determining a time of occurrence of a second characteristic value in the lateral accelerations occurring within a time range at least sufficiently large to contain said determined time limits, and

means for discriminating between a left and a right step on the basis of the order of occurrence of said current first characteristic value and said second characteristic value.

65. The apparatus of claim 64, wherein said first characteristic value is a maximum value in a group of detected acceleration values, and said second characteristic value is a minimum value of said detected accelerations, and wherein said displacement step is determined as corresponding to a right displacement step if said minimum value precedes said maximum value, and as corresponding to a left displacement step if said maximum value precedes said minimum value.

66. The apparatus of claim 53, wherein said acceleration detecting means comprises means for detecting accelerations along said vertical direction.

67. The apparatus of claim 53, wherein said characteristic determination means comprises:

means for determining a first time corresponding to an occurrence of a characteristic feature in said accelerations along a direction substantially perpendicular to a vertical direction of said pedestrian,

means for detecting accelerations along a vertical direction of said pedestrian,

means for determining a second time corresponding to an occurrence of said characteristic feature in said accelerations along a vertical direction of said pedestrian,

means for comparing said first and second times, and

means using a result of said comparison to confirm the presence of a displacement step.

68. The apparatus of claim 67, wherein said characteristic feature is a maximum acceleration value in a determined group of detected acceleration values.

69. The apparatus of claim 53, further comprising model means for distinguishing a step direction in at least one of an antero-posterior (forward-backward) sense and a lateral (left-right), said model means being adapted to recognize patterns in detected acceleration values that are representative of specific step directions.

70. The apparatus of claim 69, wherein said model means is a Hidden Markov Model.

71. The apparatus of claim 53, wherein:

said acceleration detecting means is operative to acquire successive acceleration values,

said characteristic and displacement determination means comprise;

means for determining a current peak acceleration in said successive acceleration values by means of a sliding window,

means for determining a variance of said successive acceleration values acquired between said current peak and a previous peak acceleration value,

means for comparing said variance to an adaptive threshold to detect if said pedestrian is walking or not,

means for determining whether the time interval between two successive peak acceleration values falls within a physiologically possible time interval, and

means for storing the time of acquisition of said current peak acceleration value as the time of occurrence of a detected foot impact corresponding to a displacement step.

72. The apparatus of claim 53, wherein said displacement determining means comprises means for determining a distance traveled by using at least one first model which yields a pedestrian displacement speed in response to a variance and/or a frequency of occurrence of said characteristic feature in values of said acquired accelerations, and at least a second model which correlates a pedestrian displacement speed obtained by said first model with a step length.

73. The apparatus of claim 72, wherein said first mathematical model correlates displacement speed with said variance in accordance with the following relationship:

2-dimensional relative speed=D*(variance)^E+F*frequency of steps

displacement speed=2-dimensional displacement speed+V_baro

where D, E and F are numerical coefficients from which D and F can be set equal to 0 or finite values and V_baro is the vertical velocity measured by a barometer, 2-dimensional displacement speed being obtained by multiplying the 2-dimensional relative speed by stature or the leg length according to the model which is chosen and 3-dimensional displacement speed then being computed by adding the vertical displacement V_baro to the 2-dimensional displacement speed.

74. The apparatus of claim 72, wherein said first mathematical model correlates displacement speed with either said variance or a frequency of occurrence of said characteristic feature in accordance with the following relationships:

2-dimensional relative Speed=A*(Frequency or Variance)^B+C,

displacement speed=2-dimensional displacement speed+V_baro

where A, B and C are numerical coefficients and V_baro is the vertical velocity measured by the barometer, the 2-dimensional displacement speed being obtained by multiplying the 2-dimensional relative speed by stature or the leg length according to the model which is chosen and 3-dimensional displacement speed then being computed by adding the vertical displacement V_baro to the 2-dimensional displacement speed.

75. The apparatus of claim 72, wherein said time indicator corresponds to a time interval between two successive said characteristic features, whereby:

step length=speed*time between two successive characteristic features;

or wherein said second mathematical model correlates step length with displacement speed in accordance with the following relationship;

step length=sl_o+m×

displacement speed;

where slope is a fraction of the step length which is constant and independent of speed of progression, and m is a slope of a function describing the step length as a function of displacement speed.

76. The apparatus of claim 75, wherein an initial slope value is determined with different model for a male or a female pedestrian.

77. The apparatus of claim 72, further comprising means for updating at least one parameter of said second mathematical model on the basis of external positioning data, such as data from a global positioning by satellite (GPS) system.

78. The apparatus of claim 53, wherein said displacement determining means are operative for calculating a displacement on foot and/or a displacement speed of said pedestrian.

79. The apparatus of claim 53, further comprising means for performing an azimuth computation for each step or group of steps effected to determine a position of said pedestrian.

80. The apparatus of claim 79, wherein said azimuth computation means computes an azimuth for each determined displacement step, said computation means comprising:

means for distinguishing a direction of a step between forward, backward, left and right displacement steps,

means for detecting an azimuth from a sensor carried by said pedestrian, and

means for correcting said detected azimuth with an offset angle in accordance with a distinguished of step.

81. The apparatus of claim 80, wherein said azimuth computation is performed from azimuth signals produced by magnetic sensor means.

82. The apparatus of claim 80, wherein said azimuth computation means uses azimuth signals produced by magnetic sensor means yielding raw angular data signals, said apparatus further comprising means for extracting the cosine and sine components of said raw azimuth data and filtering said cosine and sine components.

83. The apparatus of claim 80, wherein said azimuth computation means are operative to perform said computation from angular rate signals produced by a gyroscopic sensor.

84. The apparatus of claim 79, wherein said azimuth computation means comprise magnetic sensor means and other sensor means not dependent on the North magnetic field, such as gyroscope means, said apparatus further comprising:

means for comparing azimuth readings from said magnetic and said other sensor means, and

means for ignoring azimuth readings from said magnetic sensor means if said comparison step reveals a discrepancy between said readings exceeding a limit value, indicative of a significant magnetic disturbance.

85. The apparatus of claim 53, further comprising means for detecting an about turn in a displacement of said pedestrian, comprising:

means for detecting a condition in which an azimuth rate of change of said pedestrian exceeds a determined threshold,

means for determining whether said azimuth rate of change corresponds roughly to a 180°

turn,

means, operative in the affirmative, for determining whether alignments of trajectories before and after said turn are the same to within a determined discrepancy limit, and

means, operative in the affirmative, for considering that an about turn is effected.

86. The apparatus of claim 85, wherein any step made during a period in which said azimuth rate of change exceeds said determined threshold is not used to calculate a distance of displacement.

87. The apparatus of claim 85, wherein an azimuth is calculated on the basis of an average between said alignments corresponding to a forward and return path.

88. The apparatus of claim 85, wherein said about turn is considered to be effected only on the further condition that a trajectory effected after said azimuth rate of change of said pedestrian exceeds a determined threshold is statistically shorter than or equal to the straight trajectory effected before said azimuth rate of change of said pedestrian exceeds a determined threshold.

89. The apparatus of claim 53, further comprising pressure sensor means for determining an elevational component in said determined displacement.

90. The apparatus of claim 53, further comprising satellite positioning means to correct displacement information obtained through said accelerations.

91. The apparatus of claim 53, wherein said accelerations are detected by acceleration sensor means mounted on the waist of said pedestrian.

92. The apparatus of claim 53, wherein said accelerations are detected by acceleration sensor means mounted on the trunk of said pedestrian.

93. The apparatus of claim 53, wherein said accelerations are detected by using sensors of an inertial navigation system (INS).

94. The apparatus of claim 92, wherein said sensors are housed in a module together with azimuth detection means, said azimuth detection means being one of a magnetic sensor means and/orgyroscope means, and being used to acquire azimuth data.

95. The apparatus of claim 53, wherein said accelerations are detected by means of three mutually orthogonal acceleration sensors each delivering an acceleration component of a respective orthogonal axis on a separate channel.

96. The apparatus of claim 53, wherein said accelerations are detected by means of two mutually orthogonal acceleration sensors each delivering an acceleration component operatively aligned along a respective orthogonal axis, the alignment of at least one of said sensors having a component in a non vertical direction when operatively carried by said pedestrian.

97. The apparatus of claim 96, wherein at least one said axis of an accelerometer is inclined with respect to a vertical axis of said pedestrian.

98. An apparatus for pedestrian navigation operative in a dead reckoning mode, comprising:

means for detecting an evolving signal indicative of accelerations of said pedestrian in the antero-posterior (forward-backward) direction,

means for analyzing said signals to determine a variation therein conforming to predetermined constraints,

means using said variation to establish a displacement step motion and to determine displacement information comprising at least one of a speed and distance of displacement,

means for determining an azimuth of said pedestrian, and

means for combining said displacement data with said azimuth to obtain pedestrian navigation information.

99. An apparatus for pedestrian navigation operative in a dead reckoning mode, comprising:

an Inertial Navigation System (INS) serving as a source acceleration signals, said system having a motion detection sensor responsive to accelerations along the antero-posterior (forward-backward) direction of said pedestrian,

means for submitting signals from said INS to a waveform analysis to determine a step of said pedestrian, and

means for determining pedestrian navigation information on the basis of said waveform analysis.

100. The apparatus of claim 99, wherein said INS also has a motion sensor responsive to accelerations along a lateral (left-right) direction of said pedestrian, signals therefrom being submitted to a waveform analysis to determine a left or right displacement effected by said pedestrian.

101. The apparatus of claim 99, wherein said INS also has a motion sensor responsive to accelerations along a vertical direction of said pedestrian, signals therefrom being submitted to a waveform analysis to provide a confirmation of a determination of a displacement step.

102. The apparatus of claim 99, wherein said INS further comprises bearing detection means in the form of magnetometer means or gyroscope means, said means being used to obtain an azimuth of said pedestrian for the determination of said navigation information.

103. The apparatus of claim 99, wherein said INS is in the form of a module carried on the waist of said pedestrian.

104. The apparatus of claim 99, wherein said INS is in the form of a module carried on trunk of said pedestrian.