Accelerometer data compression

1. A method comprising the steps of:

receiving, by a processor, a location of a mobile device configured to be transported, carried or worn by a user determined at a plurality of times during a journey from a first location to a second location;

receiving, by the processor, acceleration values indicative of the movement of the user and/or device a plurality of times during the journey measured at a first frequency;

generating, by the processor, values representative of the measured acceleration values at a second frequency, which is lower than the first frequency, said step of generating comprising:

defining a plurality of time windows, each time window containing a plurality of measured acceleration values; and

applying a transformation to the measured acceleration values within each time window to generate a plurality of transformed values; and,

selecting, for each time window, at least one of said plurality of transformed values and/or one or more parameters derived from the plurality of transformed values to be stored;

storing: (i) the received locations and/or data derived therefrom; and (ii) the selected data derived from the acceleration values; and

transmitting the stored data from the mobile device to a remote server for use in providing a representation of the journey.

2. The method as claimed in claim 1 , wherein the acceleration values are measured using one or more accelerometers.

3. The method as claimed in claim 1 , wherein the first frequency is between 1 Hz and 20 Hz.

4. The method as claimed in claim 1 , wherein the acceleration values are stored in a data buffer.

5. The method as claimed in claim 1 , further comprising determining an absolute acceleration value indicative of the movement of the user from the measured acceleration values.

6. The method as claimed in claim 1 , wherein the plurality of time windows are defined such that a portion of one time window overlaps a portion of an adjacent time window.

7. The method as claimed in claim 1 , wherein the second frequency is between 0.1 and 2 Hz.

8. The method as claimed in claim 1 , wherein transformation applied to the measured acceleration values comprises a fast Fourier transformation.

9. The method as claimed in claim 1 , further comprising:

applying a transformation to the acceleration values within each time window to generate a frequency spectrum; and

storing one or more parameters associated with the frequency spectrum.

10. The method as claimed in claim 9 , wherein the one or more parameters associated with the frequency spectrum comprise at least one of: one or more indexed coefficients; and one or more parameters derived from the indexed coefficients.

11. The method as claimed in claim 10 , wherein said one or more parameters are selected from the group consisting of: (i) the zero index amplitude; (ii) the largest nonzero index amplitude; (iii) the index associated with the largest amplitude; and (iv) the sum of all the non-zero index amplitudes.

12. A mobile device configured to be transported, carried or worn by a user, comprising:

a receiver for determining the location of the mobile device at a plurality of times during a journey from a first location to a second location;

one or more accelerometers for measuring acceleration values indicative of the movement of the user and/or device at a plurality of times during the journey at a first frequency;

at least one processor arranged to generate values representative of the measured acceleration values at a second frequency, which is lower than the first frequency, by:

defining a plurality of time windows, each time window containing a plurality of measured acceleration values; and

applying a transformation to the measured acceleration values within each time window to generate a plurality of transformed values; and

the at least one processor being further arranged to select for each time window, at least one of said plurality of transformed values and/or one or more parameters derived from the plurality of transformed values to be stored;

at least one data storage device for storing data received from and/or derived from the receiver and the selected data derived from the one or more accelerometers; and

a transmitter for transmitting the stored data from the mobile device to a remote server for use in providing a representation of the journey.

13. The mobile device as claimed in claim 12 , wherein said one or more accelerometers comprise a three-axis accelerometer.

14. The mobile device as claimed in claim 12 , wherein the receiver comprises a global navigation satellite system (GNSS) receiver for determining the location of the user.

15. The mobile device as claimed in claim 12 , wherein the mobile device is a portable personal training device comprising a housing having a strap for securing the device to a user.

16. A non-transitory computer-readable medium storing a set of instructions which, when executed by at least one processor, causes the at least one processor to perform a method, the method executed by the set of instructions comprising:

receiving a location of a mobile device configured to be transported, carried or worn by a user determined at a plurality of times during a journey from a first location to a second location;

receiving acceleration values indicative of the movement of the user and/or device a plurality of times during the journey measured at a first frequency;

generating values representative of the measured acceleration values at a second frequency, which is lower than the first frequency, said step of generating comprising:

defining a plurality of time windows, each time window containing a plurality of measured acceleration values; and

applying a transformation to the measured acceleration values within each time window to generate a plurality of transformed values; and,

selecting, for each time window, at least one of said plurality of transformed values and/or one or more parameters derived from the plurality of transformed values to be stored;

storing: (i) the received locations and/or data derived therefrom; and (ii) the selected data derived from the acceleration values; and

transmitting the stored data from the mobile device to a remote server for use in providing a representation of the journey.

17. The computer-readable medium as claimed in claim 16 , further comprising determining an absolute acceleration value indicative of the movement of the user from the measured acceleration values.

18. The computer-readable medium as claimed in claim 16 , further comprising:

applying a transformation to the acceleration values within each time window to generate a frequency spectrum; and

storing one or more parameters associated with the frequency spectrum.

19. The computer-readable medium of claim 18 , wherein the one or more parameters associated with the frequency spectrum comprise at least one of: one or more indexed coefficients; and one or more parameters derived from the indexed coefficients.

20. The computer-readable medium of claim 19 , wherein said one or more parameters are selected from the group consisting of: (i) the zero index amplitude; (ii) the largest nonzero index amplitude; (iii) the index associated with the largest amplitude; and (iv) the sum of all the non-zero index amplitudes.