Position detecting device

1. A position detecting device comprising:

a rear projector that projects an image;

a projection screen that displays the image projected from said rear projector;

imaging means that, from a rear side of said projection screen, takes an image of light emitted from a pointer that points from a front side of said projection screen including the entire image projected on said projection screen by the projector; and

coordinate calculating means that analyzes the image taken by said imaging means to detect a two-dimensional position in a detection area where the light from said pointer is detected,

further comprising a warpage preventing member that prevents warpage of said projection screen, and a treatment for preventing light reflection is applied to a plane of incidence of said warpage preventing member where light from said rear projector is incident.

2. The position detecting device according to claim 1 , wherein said pointer includes a plurality of pointers, and said coordinate calculating means detects two-dimensional positions in the detection areas where light rays from said plurality of pointers are detected.

3. The position detecting device according to claim 2 , wherein information other than positional information and recognition information about said plurality of pointers is detected as information included in said detection areas.

4. The position detecting device according to claim 2 , wherein said imaging means includes a plurality of monochrome imaging means of a number corresponding to the number of said pointers, and said plurality of monochrome imaging means respectively comprise filters that transmit only particular wavelengths corresponding respectively to said pointers.

5. The position detecting device according to claim 1 , wherein said imaging means is decentered imaging means, and said rear projector is located approximately on a center axis of said projection screen, and said imaging means is positioned near said rear projector in such a way that no interference occurs between said imaging means and said rear projector.

6. The position detecting device according to claim 1 , wherein said imaging means takes an image of an area larger than an actually required imaging area, and said rear projector is located approximately on a center axis of said projection screen, and said imaging means is positioned near said rear projector in such a way that no interference occurs between said imaging means and said rear projector.

7. The position detecting device according to claim 6 , wherein an unnecessary area imaged by said imaging means is minimized by setting a proper combination of aspect ratios of said rear projector and said imaging means.

8. The position detecting device according to claim 1 , wherein said rear projector is located in a position shifted from a center axis of said projection screen in such a way that an optical axis of the projected image is directed toward a viewer.

9. The position detecting device according to claim 1 , wherein said pointer has a light source of invisible light.

10. The position detecting device according to claim 9 , wherein said pointer has a built-in light source of visible light associated with said invisible light emitted from said pointer.

11. The position detecting device according to claim 9 , further comprising a bending mirror that reflects visible light and transmits invisible light.

12. The position detecting device according to claim 9 , further comprising a bending mirror that reflects invisible light and transmits visible light.

13. The position detecting device according to claim 1 , wherein said imaging means is built in said rear projector.

14. The position detecting device according to claim 1 , wherein an image output timing of said rear projector and an imaging timing of said imaging means are controlled such that light of the image projected from said rear projector and the light emitted from said pointer can be distinguished from each other.