Abstract: A local positioning system (LPS) using acoustic time-of-flight and a fixed array of receivers. The LPS provides an automatic means of determining the position of a roving transmitter with respect to that of a fixed reference station based on the known relative positioning of the receivers and the times-of-flight of the pulsed signal to each receiver. The location means is local in nature and independent of any remote transmissions such as those from remote radio antennae or satellites. The LPS employs pulsed acoustic emissions and does not require a clear line of sight between the rover and the receiver. To provide a more accurate calculation of the location of the rover, the position data is adjusted for the current speed of sound and the wind velocity.

Abstract: An interactive image projection apparatus for the projection of computer generated images on a projection surface in cooperation with a light source and projection optics for projecting a beam of light from the light source onto the projection surface. The apparatus includes a substantially transparent image display device disposed in the beam of light and including means for receiving image-defining signals from a computer and producing an image based on the image-defining signals that is projected onto the projection surface in the beam of light. A touch screen, at least a portion of which is substantially transparent, is disposed in the beam of light between the image display device and the projection surface and includes means for generating a signal when touched for use as input information at the computer. Preferably, the touch screen is supported directly over the image display device.