Determining and tracking movement

1. An apparatus comprising:

a screen;

an imaging system configured to capture an image of the screen; and

a position indicating system that includes:

a housing;

a first light emitter disposed within the housing and oriented to emit light in a first direction toward the screen;

a second light emitter disposed within the housing and oriented to emit light in a second direction, the second direction being collinear with and opposite to the first direction; and

a third light emitter disposed within the housing and oriented to emit light in a third direction, the third direction being different than the first direction and the second direction;

wherein the screen is disposed between the position indicating system and the imaging system.

2. The apparatus of claim 1 , wherein the third light emitter is positioned so that a line corresponding to the third direction intersects with a line corresponding to the first direction.

3. The apparatus of claim 2 , wherein the third light emitter is oriented so that the third direction is perpendicular to the first direction.

4. The apparatus of claim 2 , wherein the third light emitter is oriented to emit light toward the screen.

5. The apparatus of claim 4 , wherein the third light emitter is oriented so that the third direction is offset from the first direction by an offset angle of less than 90 degrees.

6. The apparatus of claim 5 , wherein the third light emitter is oriented so that the third direction is offset from the first direction by an offset angle of less than 45 degrees.

7. The apparatus of claim 6 , wherein the third light emitter is oriented so that the third direction is offset from the first direction by an offset angle of between 5 degrees and 15 degrees.

8. The apparatus of claim 6 , wherein the third light emitter is oriented so that the third direction is offset from the first direction by an offset angle of less than 10 degrees.

9. The apparatus of claim 4 , further comprising a motion determining device configured to process the image of the screen to determine motion of the imaging system based on identifying intersection points of light emitted by the first light emitter and light emitted by the third light emitter.

10. The apparatus of claim 1 , further comprising a reference position indicating system that includes a reference light emitter configured to emit light toward the screen.

11. The apparatus of claim 1 , wherein the screen is curved and the second light emitter being positioned and oriented to emit light toward the screen.

12. The apparatus of claim 11 , wherein the screen has a semi-cylindrical shape.

13. An apparatus comprising:

a screen assembly including a first planar screen and a second planar screen;

an imaging system including a first camera configured to capture images of the first planar screen and a second camera configured to capture images of the second planar screen;

a position indicating system including:

a first light emitter positioned and oriented to emit light in a first direction toward the first planar screen;

a second light emitter positioned and oriented to emit light in a second direction toward the second planar screen, the second direction being collinear with and opposite to the first direction; and

a third light emitter positioned and oriented to emit light in a third direction toward the first planar screen, the third direction being different than the first direction and the second direction.

14. The apparatus of claim 13 , wherein the third light emitter is oriented so that the third direction is offset from the first direction by an offset angle of less than 45 degrees.

15. The apparatus of claim 13 , further comprising a motion determining device configured to:

process a first image to determine a first intersection point, the first intersection point corresponding to an intersection of light emitted by the first light emitter with the first planar screen;

process a second image to determine a second intersection point, the second intersection point corresponding to an intersection of light emitted by the second light emitter with the second planar screen;

process the first image to determine a third intersection point, the third intersection point corresponding to an intersection of light emitted by the third light emitter with the first planar screen;

determine a position of the position indicating system relative to the screen assembly based on the first intersection point and the third intersection point; and

determine an orientation of the position indicating system relative to the screen assembly based on the first intersection point, the second intersection point, and the third intersection point.

16. The apparatus of claim 15 , wherein the motion determining device being configured to determine a position of the position indicating system relative to the screen assembly based on the first intersection point and the third intersection point includes the motion determining device being configured to:

determine an identifier for the position indicating system;

retrieve an offset angle compensation factor associated with the identifier of the position indicating system;

determine a distance between the first intersection point and the third intersection point; and

determine a distance from the first planar screen to the position indicating system based on the retrieved offset angle compensation factor and the determined distance between the first intersection point and the third intersection point.