Digital scan converters

A digital scan converter, comprising means for receiving response signals from a mobile surveillance apparatus;

• means for digitizing the said response signals and providing digital indications of the positions from which the response signals have been returned, in terms of coordinates related to the instantaneous position of the mobile surveillance apparatus;
• a position register for receiving and storing digital indications of the said instantaneous position;
• a random-access memory having a multitude of addressible locations in which the digitized response signals may be stored;
• input scan means for directing the digitized response signals into locations in the random-access memory whose addresses are derived from the said coordinates and the contents of the position register so that each digitized response signal is directed to a location whose address is a function of coordinates of the position from which it was returned to the surveillance apparatus;
• output scan means for reading out signals from the random-access memory according to a raster scan starting from a location whose address is a function of the contents of the position register;
• and video display means for providing a visual display in response to the signals read out by the output scan means.