1
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The following data is captured from the magnetic sensor of a device. This data has a time factor. The device is at times in motion and other times still

How can one detect (using formula) if there is a significant change in the magnetic field so as to differentiate between the device being in motion and the device being still.

Columns are as follows (x signal, y signal, z signal, timestamp) Note: we may combine x,y,z into one field using a formula sqrt(x^2 + y^2 + z^2)

            -12.718201, -6.2164307, 62.046814   ,  1538194954316
            -43.415833, -12.576294, 62.527466   ,  1538195258969
            -19.099426, -20.405579, 53.93982    ,  1538195608542
            36.384583, -2.8259277, 125.75989    ,  1538196141515
            3.7750244, -52.175903, 7.0632935    ,  1538196696008
            -57.774353, -0.17547607, -34.48639  ,  1538197016697
            -19.52362, -33.039856, -11.776733   ,  1538197575860
            -14.483643, 7.3242188, 49.07837 ,  1538197889355
            -61.299133, -10.044861, -10.276794  ,  1538198275366
            -7.598877, -27.565002, 38.954163    ,  1538198604350
            6.6818237, -19.360352, 45.41931 ,  1538198916440
            5.3466797, -20.59021, 44.63806  ,  1538199218767
            4.4311523, -21.595764, 43.948364    ,  1538199662156
            20.075989, -32.650757, 91.15448 ,  1538200082654
            14.196777, -17.500305, 56.92444 ,  1538200408499
            14.120483, -17.33551, 56.60858  ,  1538200722135
            14.961243, -16.825867, 57.299805    ,  1538201524650
            14.060974, -17.636108, 55.8136  ,  1538202502702
            16.416931, -10.900879, 59.924316    ,  1538203467708
            34.70,  1538, -42.219543, -12.271118    ,  1538203770037
            26.541138, -33.729553, 42.088318    ,  1538204432606
            -2.9037476, -46.420288, 27.973938   ,  1538205300693
            28.746033, -42.57965, 12.928772 ,  1538205775288
            27.441406, -40.000916, 6.7489624    ,  1538206205786
            39.141846, -42.070007, 1.7837524    ,  1538206565996
            11.735535, -40.135193, -8.190918    ,  1538207068072
            33.441162, -34.03015, 4.109192  ,  1538207429684
            30.140686, -35.84442, 4.019165  ,  1538207922966
            -4.823303, -46.780396, 26.098633    ,  1538208284175
            -8.934021, -47.27478, 23.068237 ,  1538208716472
            56.64673, -32.35016, 3.5079956  ,  1538209153066
            0.8468628, 21.784973, 56.489563 ,  1538209521175
            1.5808105, 22.340393, 56.56433  ,  1538209824603
            0.7720947, 22.7005, 55.604553   ,  1538210815860
            0.2166748, 24.18518, -59.835815 ,  1538211721937
            -0.05340576, 23.62976, -59.925842   ,  1538212665907
            -11.079407, 23.675537, 45.49408 ,  1538213486000
            -8.4991455, 36.860657, 44.06891 ,  1538213789633
            -0.05340576, 22.219849, 56.89392    ,  1538214091858
            0.35095215, 22.399902, 55.79834 ,  1538214416776
            -14.604187, 33.54492, 45.7489   ,  1538214757598
            2.0462036, 21.679688, 57.658386 ,  1538215059916
            2.2705078, 22.070312, 56.217957 ,  1538215463919
            4.6417236, 23.464966, -55.485535    ,  1538215776043
            4.9560547, 23.480225, -55.770874    ,  1538216078469
            -6.3095093, 44.000244, 38.36975 ,  1538216396388
            10.08606, -19.270325, 65.608215 ,  1538263082893
            10.08606, -19.270325, 65.608215 ,  1538263082893
            15.606689, -14.515686, 55.18341 ,  1538263760629
            2.7053833, -24.6109, 38.14392   ,  1538264179725
            2.7053833, -24.6109, 38.14392   ,  1538264179725
            3.9367676, -24.624634, 38.7146  ,  1538264484521
            3.9367676, -24.624634, 38.7146  ,  1538264484521
            4.0115356, -23.980713, 38.684082    ,  1538264830196
            4.0115356, -23.980713, 38.684082    ,  1538264830196
            3.3660889, -25.645447, 37.709045    ,  1538265135334
            3.3660889, -25.645447, 37.709045    ,  1538265135334
            3.4866333, -24.549866, 38.77411 ,  1538265439125
            3.4866333, -24.549866, 38.77411 ,  1538265439125
            3.9520264, -24.760437, 38.323975    ,  1538265738751
            3.9520264, -24.760437, 38.323975    ,  1538265738751
            3.90625, -24.264526, 38.789368  ,  1538266042583
            3.90625, -24.264526, 38.789368  ,  1538266042583
            4.0115356, -24.925232, 38.128662    ,  1538266361898
            4.0115356, -24.925232, 38.128662    ,  1538266361898
            4.0863037, -24.085999, 38.414   ,  1538266666426
            4.0863037, -24.085999, 38.414   ,  1538266666426
            4.1015625, -23.905945, 38.789368    ,  1538266972752
            4.1015625, -23.905945, 38.789368    ,  1538266972752
            3.6514282, -24.685669, 38.15918 ,  1538267571704
            8.480835, -22.03064, 50.48828   ,  1538267875317
            8.570862, -20.87555, 49.96338   ,  1538268178843
            8.511353, -21.040344, 50.02289  ,  1538268482369
            8.976746, -21.220398, 50.143433 ,  1538268785994
            -1.4938354, -19.239807, 49.394226   ,  1538269583765
            9.965515, -21.174622, 34.918213 ,  1538270525838
            10.626221, -20.994568, 34.214783    ,  1538271159386
            11.735535, -20.080566, 35.264587    ,  1538271788831
            11.557007, -19.570923, 36.149597    ,  1538272087257
            9.516907, -21.76056, 34.709167  ,  1538272403782
            9.486389, -20.890808, 35.23407  ,  1538272702208
            9.306335, -21.534729, 35.24933  ,  1538273006933
            9.231567, -21.76056, 34.843445  ,  1538273314658
            8.840942, -21.775818, 35.23407  ,  1538273619714
            9.156799, -22.30072, 34.843445  ,  1538273927994
            8.992004, -22.239685, 35.534668 ,  1538275489504
            8.557129, -22.450256, 34.36432  ,  1538275787028
            8.390808, -22.929382, 36.523438 ,  1538276691072
            7.6705933, -22.975159, 36.98883 ,  1538277352472
            7.7163696, -22.735596, 36.883545    ,  1538278611579
            7.852173, -23.57483, 37.31842   ,  1538279282128
            2.4368286, 21.31958, -56.536865 ,  1538280332534
            2.7053833, 21.995544, -56.37207 ,  1538280937891
            2.6168823, 22.340393, -56.565857    ,  1538281844967
            2.9907227, 22.48993, -57.510376 ,  1538282750451
            -26.54419, 26.434326, 44.503784 ,  1538283048971
            24.066162, 5.104065, 61.079407  ,  1538283383594
            23.76709, 5.4504395, 61.33423   ,  1538283863574
            23.87085, 1.3549805, 60.598755  ,  1538284538406
            24.336243, 1.2054443, 61.288452 ,  1538285494179
            24.020386, 1.5945435, 61.228943 ,  1538286514128
            -17.408752, 34.71527, 45.133972 ,  1538287869792
            24.276733, 4.7454834, -59.74579 ,  1538288474649
            24.14093, 4.234314, -60.375977  ,  1538289084002
            -12.579346, 40.87982, 40.12451  ,  1538289775226
            -16.358948, 32.974243, 46.273804    ,  1538290103548
            7.446289, -15.234375, 49.768066 ,  1538301760672
            11.302185, -1.0757446, -55.036926   ,  1538302063111
            41.15143, -20.500183, -38.746643    ,  1538302490209
            49.23706, 8.360291, 19.708252   ,  1538302955188
            55.14679, 5.899048, 0.55389404  ,  1538303257514
            10.296631, -51.96991, -5.836487 ,  1538303592431
            5.555725, -52.149963, 3.8986206 ,  1538303913855
            15.156555, -48.519897, -0.105285645 ,  1538304216080
            55.252075, 0.78430176, 4.5440674    ,  1538304513209
            14.901733, -6.6848755, -50.31128    ,  1538304814535
            17.556763, -4.9453735, -49.531555   ,  1538305258231
            17.07611, -4.43573, -50.341797  ,  1538305885274
            16.80603, -4.0145874, -50.656128    ,  1538306849839
            16.911316, -5.064392, -50.35553 ,  1538307934275
            2.7069092, -9.054565, -54.196167    ,  1538311487005
            7.762146, -7.044983, -55.111694 ,  1538318042202
            8.226013, -7.029724, -54.571533 ,  1538318348333
            28.881836, -20.724487, 34.6344  ,  1538322159796
            55.836487, 2.0751953, 4.034424  ,  1538322473121
            55.40161, 0.74005127, 2.1881104 ,  1538322775548
            55.656433, -0.44555664, -0.6011963  ,  1538323077773
            6.111145, -53.260803, -5.041504 ,  1538323403594
            4.6569824, -53.260803, 3.237915 ,  1538323706020
            4.147339, -52.915955, 1.7837524 ,  1538324008146
            16.056824, -49.031067, -14.460754   ,  1538324310571
            16.671753, -38.830566, -33.00171    ,  1538324607800
            12.696838, -42.234802, -29.986572   ,  1538324904227
            15.2908325, -42.715454, -28.831482  ,  1538325200955
            15.802002, -41.410828, -30.33142    ,  1538325504501
            25.115967, -37.58545, -30.421448    ,  1538325806906
            26.000977, -31.40564, -36.106873    ,  1538326109333
            38.82599, 8.479309, -38.687134  ,  1538326411561
            2.6763916, -15.1901245, 54.553223   ,  1538326714988
            11.091614, -11.425781, 55.34973 ,  1538327101994
            5.2719116, -13.525391, 54.733276    ,  1538327760734
            3.5461426, -13.510132, 54.808044    ,  1538328693404
            3.7109375, -55.78003, -2.0858765    ,  1538328998328
            2.5558472, -56.289673, -4.470825    ,  1538329304253
            2.0767212, -55.97534, -6.826782 ,  1538329613277
            56.106567, -2.8305054, -1.7562866   ,  1538329943497
            6.126404, -55.23987, -6.3308716 ,  1538330245922
            4.685974, -54.699707, -10.140991    ,  1538330548249
            55.911255, -5.769348, 2.5482178 ,  1538330850574
            39.11133, 12.739563, -37.12616  ,  1538331152901
            -45.06836, 0.14038086, -38.160706   ,  1538331455232
            17.390442, 23.554993, 55.903625 ,  1538347134220
            -20.439148, 7.460022, -38.430786    ,  1538347747579
            7.8216553, -1.361084, 38.668823 ,  1538348220161
            7.8216553, -1.361084, 38.668823 ,  1538348220161
            -18.263245, -5.529785, 44.413757    ,  1538349874458
            -16.912842, -4.2099, 43.933105  ,  1538350264958
            -16.299438, -3.4606934, 44.248962   ,  1538350888812
            -17.408752, -3.2043457, 43.75305    ,  1538351816582
            -17.21344, -2.859497, 43.963623 ,  1538352751656
            -15.0390625, 18.469238, 39.65912    ,  1538353830887
            14.840698, 1.8951416, -48.661804    ,  1538354344165
            14.945984, 1.9851685, -47.98584 ,  1538355025003
            -20.063782, 19.309998, 33.494568    ,  1538355508777
            14.196777, -1.2557983, -48.435974   ,  1538355811207
            14.256287, -1.1352539, -48.616028   ,  1538356307085
            45.20111, 5.2993774, -1.725769  ,  1538356801760
            13.490295, -4.135132, -48.690796    ,  1538357330936
            13.116455, -4.4662476, -48.616028   ,  1538357983879
            -21.833801, 37.864685, 17.36908 ,  1538358586625
            -20.904541, 34.205627, 36.98883 ,  1538376675008
            -20.904541, 34.205627, 36.98883 ,  1538376675008
            -20.904541, 34.205627, 36.98883 ,  1538376675008
            -54.803467, -13.960266, 19.213867   ,  1538377228431
            12.892151, 18.515015, 49.409485 ,  1538377529758
            -19.299316, -15.115356, -50.37079   ,  1538377828945
            27.410889, 30.439758, 17.173767 ,  1538378132271
            33.14209, -121.65985, 58.439636 ,  1538378799010
            25.29602, -19.210815, -1.9210815    ,  1538379096134
            31.70166, 18.455505, -25.186157 ,  1538379398086
            -13.418579, -1.8707275, -58.546448  ,  1538420544161
            -13.418579, -1.8707275, -58.546448  ,  1538420544161
            -13.62915, -1.84021, -58.605957 ,  1538421151809
            -13.62915, -1.84021, -58.605957 ,  1538421151809
            -12.849426, -1.4953613, -58.410645  ,  1538422062386
            -12.849426, -1.4953613, -58.410645  ,  1538422062386
            -11.888123, -1.045227, -58.39691    ,  1538422970267
            -11.888123, -1.045227, -58.39691    ,  1538422970267
            -13.508606, 2.2994995, -58.621216   ,  1538426539190
            -13.508606, 2.2994995, -58.621216   ,  1538426539190
            -21.218872, 21.424866, 44.892883    ,  1538429695519
            -21.218872, 21.424866, 44.892883    ,  1538429695519
            23.81134, 1.1001587, -54.286194 ,  1538430409350
            23.81134, 1.1001587, -54.286194 ,  1538430409350
            -18.188477, 41.56952, 33.374023 ,  1538430735066
            -18.188477, 41.56952, 33.374023 ,  1538430735066
            56.570435, 4.849243, -1.876831  ,  1538431244046
            56.570435, 4.849243, -1.876831  ,  1538431244046
            -36.819458, 29.225159, 35.038757    ,  1538431665892
            -36.819458, 29.225159, 35.038757    ,  1538431665892
            -121.02814, -63.459778, -74.16077   ,  1538432237155
            -121.02814, -63.459778, -74.16077   ,  1538432237155
            5.4214478, -22.390747, -32.70111    ,  1538432879063
            5.4214478, -22.390747, -32.70111    ,  1538432879063
            22.805786, -68.98041, -22.291565    ,  1538433213184
            22.805786, -68.98041, -22.291565    ,  1538433213184
            15.306091, 17.480469, 71.15936  ,  1538433516174
            15.306091, 17.480469, 71.15936  ,  1538433516174
            -14.663696, -52.81067, 18.148804    ,  1538434199096
            -14.663696, -52.81067, 18.148804    ,  1538434199096
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  • $\begingroup$ What are the units of the signals, including time? $\endgroup$ – Adrian Keister Dec 10 '18 at 14:54
  • $\begingroup$ the time is in milliseconds since Unix Epoch, the x,y,z are signal strengths $\endgroup$ – hyena Dec 13 '18 at 7:50
  • $\begingroup$ Thanks for the time units. You have not yet provided the units for the other signals, since "signal strengths" is not a physical unit. Are we talking magnetic field strength, like Federico assumed? In that case the units might be Teslas. What we need here is a recognized physical unit for the three other signals. $\endgroup$ – Adrian Keister Dec 13 '18 at 13:56
  • 1
    $\begingroup$ am trying to use a magnetic sensor as opposed to accelerometer because of power consumption, as the device will be getting this values every ~ 5 min $\endgroup$ – hyena Dec 14 '18 at 21:40
  • 1
    $\begingroup$ also accelerometer is more suited for small changes where us the magnetic field could be used to infer that the device has moved from one location to another. $\endgroup$ – hyena Dec 14 '18 at 21:44
1
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Since we don't have any information on the orientation of the device, I only looked at the norm of the magnetic field. Here is a plot: enter image description here

As you can see, there are intervals over which the norm of the magnetic field is relatively constant (from 50 to 100 and around 130).

EDIT

Given we have not much additional information on the underlying physical process, the most reasonable thing to do seems to me to just look at some moving variances (see for instance here, here, here, here). What I mean is that you fix some window timeframe and look at how much the data oscillates in that window. If the oscillation is sufficiently low, then the field you are measuring is almost constant in norm, which could mean that you are almost stationary.

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  • $\begingroup$ am assuming one axis should be the time stamp, correct me if am wrong $\endgroup$ – hyena Dec 13 '18 at 7:51
  • $\begingroup$ Oh yes sure, sorry. The horizontal axis is time, the vertical is the norm of the field $\endgroup$ – Federico Dec 13 '18 at 14:28
  • $\begingroup$ probably i can use several moving variances, where i can treat one of the variance as a signal line $\endgroup$ – hyena Dec 14 '18 at 21:49
  • 1
    $\begingroup$ i took your suggestion and used Knime to get some Moving Averages . the smallest duration is 15 min and the highest duration is 2 hour, plotting a graph using this two lines, i get the lines crossing close to the times, the device was on the move. i have put a link to the Kinme export file. dropbox.com/s/dui57q33a1pdooe/… $\endgroup$ – hyena Dec 17 '18 at 9:42
  • $\begingroup$ here is a link to the data magnetic signal dropbox.com/s/at1mwuc9osssq5j/… the fields are [guid,source,x,y,z,accuracy,timestamp] the time stamp is in milliseconds since Unix Epoch $\endgroup$ – hyena Dec 18 '18 at 7:36

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