Digital scan converter

Abstract

Abstract 1388233 Radar; scan conversion HUGHES AIRCRAFT CO 21 May 1973 [2 June 1972] 24128/73 Heading H4D and H4F Video signals resulting from scanning a scene in a first pattern, e.g. those from a standard pulse radar 10a with an antenna rotating in azimuth, are displayed using a second, different pattern, by first converting the analogue video signals to digital form (10b) and storing the digital signals-e.g. one radial line at a timein a buffer store 10c, in positions corresponding to the first scan pattern. Each such position is converted to its equivalent in the second scan pattern and the converted positions used to store the digital signals in a random access memory 12 in accordance with the second pattern. When a whole field has been thus converted and stored, memory 12 is read out in accordance with the second pattern into a display 33, via a digitial to analogue converter 32, the display being scanned according to the second pattern. In the radar display shown, the azimuth # of the antenna is represented by an analogue signal fed to an analogue to digital converter 23. Read-only memories 15 and 16 produce digital signals representing Sin 0 and Cos # respectively which are fed to one input of respective multipliers 17, 19. The other inputs of the multipliers are fed by range ramp counter 18 with a digital representation of the range R being scanned. The range pulses feeding counter 18 are also used in controlling the storage positions in buffer 10c. The mulipliers 17, 19 thus give digital outputs respectively representing the cartesian co-ordinates X, Y of the second TV raster type pattern, equivalent to the radial co-ordinates R, 0 of the first pattern viz. X = R sin 0, Y = R cos #. The outputs are fed, via mode switches S-M in the position shown and address switches S-A in the position not shown, to the memory 12 to control the read-in of the data stored in buffer 10c. When a whole field has been stored in memory 12, switch S-A is positioned as shown and readout signals from counter 13 read out the data in memory 12, line element by line element, and line by line, according to the second pattern. The counter 33 also controls the sweep circuits for the CRT display tube 33. If the radar signals are supplied according to a type B scani.e. orthogonal, range/azimuth axes-multipliers 15 and 16 are by-passed and the R, # digital signal are fed directly to second input terminal of mode switch S-M

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