Sensing direction and distance

1. An optical sensor comprising:

a. a rectangular array of at least four photodetector cells of substantially equal size;

b. an opaque mask affixed over said array, said opaque mask defining a substantially rectangular aperture centrally positioned over said at least four photodetector cells for admitting light onto only a portion of the surface of each of said at least four photodetector cells,

wherein the optical sensor is configured to determine a bearing angle to a source of the light admitted through the aperture based on a difference in light intensity received at the at least four photodetector cells.

2. An optical sensor according to claim 1 , wherein said aperture is substantially equal in size to one of said photodetector cells.

3. An optical sensor according to claim 2 , further comprising a filter for filtering light admitted onto the surface of said photodetector cells.

4. An optical sensor according to claim 1 , further comprising circuitry for calculating at least two orthogonal bearing angles to the source of light admitted onto the surface of said photodetector cells.

5. The optical sensor of claim 2 , wherein said aperture is square.

6. The optical sensor of claim 3 , wherein said opaque mask is printed on said filter.

7. The optical sensor of claim 3 , wherein said filter is an infra-red pass filter.

8. The optical sensor of claim 1 , wherein said aperture is positioned to expose substantially equal portions of said photodetector cells.

9. The optical sensor of claim 1 , wherein said array of photodetectors comprise a first, a second, a third, and a fourth photodetector, and wherein said optical sensor determines first and second bearing angles between the sensor and an optical source, wherein said first bearing angle is determined based on the difference between the sum of the output of the first and third photodetectors and the sum of the second and fourth photodetectors and wherein said second bearing angle is determined based on the difference between the sum of said first and second photodetectors and the sum of said third and fourth photodetectors.

10. A method for determining the direction of a point-source-like emitter of light comprising:

a. providing a rectangular array of at least four photodetector cells of substantially equal size and an opaque mask affixed over said array, said opaque mask defining a substantially rectangular aperture for admitting light onto only a portion of the surface of each of said at least four photodetector cells, wherein said aperture is centrally positioned over said rectangular array; and

b. determining a bearing angle of a source of light admitted through the aperture onto the surface of said photodetector cells comprising analyzing the intensity of light received on said array from said point-source-like emitter in order to determine a difference in light intensity received at the at least four photodetector cells.

11. The method of claim 10 , wherein said aperture is substantially equal in size to one of said photodetector cells.

12. The method of claim 11 , further comprising providing a filter for filtering light admitted onto the surface of said photodetector cells.

13. The method of claim 10 , further comprising calculating at least two orthogonal bearing angles of the source of light admitted onto the surface of said photodetector cells.

14. The method of claim 11 , wherein said aperture is square.

15. The method of claim 12 , wherein said opaque mask is printed on said filter.

16. The method of claim 12 , wherein said filter is an infra-red filter.

17. The method of claim 10 , wherein said aperture is positioned to expose substantially equal portions of said photodetector cells.

18. The method of claim 10 , wherein said array of photodetectors comprise a first, a second, a third, and a fourth photodetector, and further comprising determining first and second bearing angles between the array of photodetectors sensor and an optical source, wherein said first bearing angle is determined based on the difference between the sum of the output of the first and third photodetectors and the sum of the second and fourth photodetectors and wherein said second bearing angle is determined based on the difference between the sum of said first and second photodetectors and the sum of said third and fourth photodetectors.

19. A tracking system comprising:

a. a transmitting unit comprising an optical emitter;

b. a receiving unit comprising an optical sensor adapted to receive signals from said optical emitter, the optical sensor comprising a rectangular array of at least four photodetector cells and an opaque mask having a central rectangular aperture for admitting light onto a portion of the surface of each of said at least four photodetector cells, wherein the optical sensor is configured to determine a bearing angle to a source of the admitted light through the aperture based on a difference in light intensity received at the at least four photodetector cells;

a. an acoustic emitter mounted on said transmitting unit or said receiving unit;

b. an acoustic receiver mount on a different one of said transmitting unit or said receiving unit from said acoustic emitter; and

c. a processor that determines a vector direction and a range between the receiving unit and the transmitting unit based on said received optical and acoustic signals.

20. The optical sensor of claim 1 further comprising a decoder for decoding encoded optical signals received at said sensor.

21. The optical sensor of claim 20 , wherein said optical signals are received through a rectangular array.

22. The optical sensor of claim 1 , wherein said optical sensor system lacks an image sensor and an image processor.

23. A method for determining a vector between a receiving unit and an emitter unit comprising:

a. receiving, at a receiving unit comprising an array of at least four photodetector cells with an aperture, a first optical signal from a point-source-like emitter attached to a first emitter unit;

b. analyzing a pattern on the array of light intensity of the received optical signal from the emitter;

c. determining a first coordinate of said vector by determining a difference in light intensity received at a first grouping of cells in said array and at a second grouping of cells in said array; and

d. determining a second coordinate of said vector by determining a difference in light intensity received at a third grouping of cells in said array and a fourth grouping of cells in said array.

24. The method of claim 23 , further comprising:

a. simultaneously with receiving said first optical signal, receiving, at said array,

a second optical signal from a point-source-like emitter attached to a second emitter unit;

b. distinguishing said second optical signal from said first optical signal using a multiple access scheme selected from the group of time-division-multiple-access, code-division-multiple-access and frequency-division-multiple-access; and

c. determining a vector between said receiving unit and said second emitter unit based on said distinguished second optical signal.

25. The method of claim 23 , further comprising determining a range from said receiving unit to said first emitter unit by calculating an ultrasonic time of flight based on an ultrasonic signal received from said first emitter unit and said first optical signal.

26. A tracking system comprising:

a. a receiving unit comprising an array of at least four photodetector cells with an aperture;

b. a first point-source-like emitter;

c. a data processing unit adapted to analyze a pattern on the array of light intensity of a received first optical signal from said first emitter, and to determine a first coordinate of a vector between said receiving unit and said first emitter by determining a difference in light intensity received at a first grouping of cells in said array and at a second grouping of cells said array, and to determine a second coordinate of said vector by determining a difference in light intensity received at a third grouping of cells in said array and a fourth grouping of cells in said array.

27. The system of claim 26 , further comprising a second point-source-like emitter, wherein said data processing unit is adapted to distinguish a second optical signal received from said second emitter from said first optical signal received from said first emitter using a multiple access scheme selected from the group of time-division-multiple-access, code-division-multiple-access and frequency-division-multiple-access, and to determine a vector between said receiving unit and said second emitter based on said distinguished second optical signal.