Abstract: A projection display system comprises a presentation computer (1) which generates images which are projected onto a screen (4) using a projector (3) controlled over a line (2) by the computer (1). A video camera (5) views the screen and a laser pointer (8) is supplied for pointing at the screen (4). An interaction computer (7) analyses the signal produced by the video camera (5) to determine the position of peak value in a frame to locate the point at which the laser pointer (5) is pointed. The laser pointer (6) is provided with buttons (10) which perform conventional computer mouse button functions. The state of the buttons (10) may be signalled to the computer (7) over an infra red link (9).

Abstract: The invention relates to a device for producing x-y coordinate addresses for a picture screen comprising a force-sensitive operating plate (3) influencing force measuring sensors (13a, 13b, 15a, 15b). The coordinates of points on the plate surface (23) are converted, when a force is exerted on these points, by the force measuring sensors (13a, 13b, 15a, 15b) into electrical signals, which correspond to an x-y coordinate address, which is accurately identical to the geographical place of the pressure point of the picture screen. The operating plate (3) has first side edges (17, 17b) arranged approximately parallel and opposite to each other and second side edges (19a, 19b) shifted by about 90.degree. with respect to the first side edges and also arranged parallel and opposite to each other. Auxiliary plates (103, 203) are arranged behind the opeating plate (3) in planes parallel to it.