Acoustic navigation method

1. An information processing apparatus comprising:

circuitry configured to

detect a current location of the information processing apparatus;

obtain a direction of a destination from the detected current location as a target direction;

detect a facial orientation of a user wearing a headphone unit connected to the information processing apparatus via a wired or wireless connection in relation to a reference orientation based on outputs of a geomagnetic sensor and an acceleration sensor connected to the headphone unit;

obtain a relative target angle based on a difference between the target direction and the user's facial orientation; and

generate sound to be output by the headphone unit based on the obtained relative target angle.

2. The information processing apparatus of claim 1 , wherein

the circuitry is configured to generate sound in a predetermined mode indicating that the user's facial orientation coincides with the target direction when the relative target angle is included in an angle range including 0 degrees.

3. The information processing apparatus of claim 1 , wherein

the circuitry is configured to generate sound in a first mode when the relative target angle is in a first angle range, and generate sound in a second mode, which is different from the first mode, when the relative target angle is outside of the first angle range and included in a second angle range.

4. The information processing apparatus of claim 3 , wherein

the headphone unit includes left and right earphones, and

the circuitry is configured to generate the sound by changing a volume of the left or right earphone based on whether the target direction is on the user's right side or left side when the relative target angle is outside of the first angle range and included in the second angle range.

5. The information processing apparatus of claim 3 , wherein

the circuitry is configured to generate sound in a third mode when the relative target angle is included in a third angle range corresponding to a rear side of the user's facial orientation.

6. The information processing apparatus of claim 1 , wherein the circuitry is further configured to:

obtain distance from the current location to the destination; and

change the sound output from the headphone unit to another mode based on the obtained distance.

7. The information processing apparatus of claim 1 , wherein the circuitry is configured to:

obtain a horizontal plane based on a gravity vector obtained based on output of the acceleration sensor;

obtain the reference orientation by projecting a geomagnetic vector obtained from an output of the geomagnetic sensor on the horizontal plane;

determine a direction of a straight line where a side face of the headphone unit which is in contact with the user's ear or a plane parallel to the side face intersects with the horizontal plane to be the facial orientation; and

based on an angle θd as to the reference orientation of the target direction, and an angle θf as to the reference orientation of the facial orientation, obtain a relative target angle θx that the target direction makes up as to the user's facial orientation.

8. The information processing apparatus of claim 1 , wherein the circuitry is configured to:

obtain a horizontal plane based on a gravity vector obtained based on an output of the acceleration sensor;

obtain the reference orientation by projecting a geomagnetic vector obtained from an output of the geomagnetic sensor on the horizontal plane;

project a forward direction of the headphone unit on the horizontal plane as the facial orientation; and

based on an angle θd as to the reference orientation of the target direction, and an angle θf as to the reference orientation of the facial orientation, obtain a relative target angle θx that the target direction makes up as to the user's facial orientation.

9. The information processing apparatus of claim 7 , wherein the circuitry is configured to:

control outputting a notification to the user prompting the user to perform an action to nod the user's head in a front direction; and

based on an output of the acceleration sensor in a state before nodding and in a state of a maximum nodding angle, obtain an error between the forward direction of the headphone unit and the user's facial orientation; and

correct the user's facial orientation based on the error.

10. The information processing apparatus of claim 1 , wherein

the circuitry is configured to obtain the target direction based on a latitude longitude direction of the destination obtained using a map database, and latitude longitude information of the current location.

11. The information processing apparatus of claim 1 , wherein the circuitry is configured to:

obtain a plurality of target directions;

obtain a plurality of relative target angles based on the plurality of target directions; and

generate different sounds to be output by the headphone unit with regard to each of the plurality of relative target angles.

12. The information processing apparatus of claim 11 , wherein the circuitry is configured to:

obtain additional information relating to a destination existing in the plurality of target directions; and

control the headphone unit to play, when a determination is made based on output of the acceleration sensor that the user stops to face one direction of the plurality of target directions, additional information relating to a destination corresponding to the one direction of the plurality of target directions using an audio message.

13. The information processing apparatus of claim 12 , wherein the circuitry is further configured to select, after starting acoustic navigation regarding the plurality of target directions and narrowing the plurality of target directions to one target direction, the one target direction according to a predetermined condition.

14. The information processing apparatus of claim 13 , wherein the circuitry is configured to stop subsequent acoustic navigation regarding other of the plurality of target directions when the plurality of target directions has been narrowed to one target direction.

15. An information processing method performed by an information processing apparatus, the method comprising:

detecting a current location of the information processing apparatus;

obtaining a direction of a destination from the detected current location as a target direction;

detecting a facial orientation of a user wearing a headphone unit connected to the information processing apparatus via a wired or wireless connection in relation to a reference orientation based on outputs of a geomagnetic sensor and an acceleration sensor connected to the headphone unit;

obtaining a relative target angle based on a difference between the target direction and the user's facial orientation; and

generating sound to be output by the headphone unit based on the obtained relative target angle.

16. A non-transitory computer-readable medium including computer program instructions, which when executed by an information processing apparatus, cause the information processing apparatus to:

detect a current location of the information processing apparatus;

obtain a direction of a destination from the detected current location as a target direction;

detect a facial orientation of a user wearing a headphone unit connected to the information processing apparatus via a wired or wireless connection in relation to a reference orientation based on outputs of a geomagnetic sensor and an acceleration sensor connected to the headphone unit;

obtain a relative target angle based on a difference between the target direction and the user's facial orientation; and

generate sound to be output by the headphone unit based on the obtained relative target angle.