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Inferring Horizontal Device Orientation from an Accelerometer Signal



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2009 International Symposium on Wearable Computers Which way am I facing Inferring horizontal device orientation from an accelerometer signal Kurt Partridge Bo Begole Palo Alto Research Center 3333 Coyote Hill Road Palo Alto CA 94304 kurt bo parc com Kai Kunze Paul Lukowicz Embedded Systems Lab University Passau Passau Germany first lastname uni passau de Abstract z first pca component We present a method to infer the orientation of mobile device carried in a pocket from the acceleration signal acquired when the user is walking Whereas previous work has shown how to determine the the orientation in the vertical plane angle towards earth gravity we demonstrate how to compute the orientation within the horizontal plane To validate our method we compare the output of our method with GPS heading information when walking in a straight line On a total of 16 different orientations and traces we have a mean difference of 5 degrees with 2 5 degrees standard deviation y gravity vector x Figure 1 Accelerometer coordinate system in relation to the gravity vector vertical component and the walking direction infered using pca 2 Approach 1 Introduction We base the approach on three assumptions The user walks facing forward The device is placed in a trouser s pocket Our approach should also yield similar results on the persons torso or similar on body placements However we did not test them in this paper We apply our approach on a walking segment in which the user walked fairly straight As already described by Mizel 5 one can estimate the gravity vector component of a 3 axis accelerometer We use a slight variation of this method to get the acceleration axis parallel to the persons torso We apply a sliding window over over all 3 axis If the variance of all axis is close to 0 and the magnitude approaches 9 81 m s2 the signal is very likely to be dominated by the vertical orientation component Using this heuristic we infer the vertical component Now we project the accelerometer signal



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