Abstract: A method of determining distances and angular positions of stationary and moving objects (3), for example in an area to be monitored in connection with for instance swing doors. The determination is done by means of triangulation where light, which in the main part is collimated, is transmitted (1) into the area at different angles and in a certain sequence. The reflected light is correspondingly registered on a position-sensitive sensor (5) which is positioned at a certain distance from the transmitter (1). The position (5a, 5b), where the reflected light falls on the sensor (5), represents the distance, and the moment when the light is received represents the angular position of the detected object. The values are compared to stored reference values which change when the angle of the door's opening is changed.

Abstract: The position of a transverse crease line of a moving packing web is sensed in that light reflected from the web and emanating from a laser directed perpendicularly to the web is received by photo detectors from two directions in the direction of movement of the web and under an angle of for example 60.degree. in relation to the light beam directed to the web. The electrical measuring signal emanating from the photo detectors is compared in an electronic signal processor with a reference signal, which is stored in the processor and is representative of a reference crease line. A crease line is indicated when the value of a correlation signal, which constitutes a calculation of conformity between the measuring signal and the reference signal, reaches a maximum. In a corresponding way, the position of a longitudinal crease line can be sensed.