A method and apparatus for converting polar format radar video data into a horizontal raster format output to a TV monitor. Radar video data comprises radar video pixels each having an associated intensity value and a polar coordinate in a raster display. The TV monitor includes a display screen including a plurality of pixels wherein each pixel has a corresponding X,Y address. The apparatus and method of the invention comprises steps or apparatus for storing the radar video pixels, translating X,Y addresses into corresponding angular and radial coordinates, scanning the storage means using the translated X,Y address and interpolating a radar intensity value for the translated X,Y address. The radar video pixels are indexed by radial and angular coordinates. The scanning process includes accessing at least four radar video pixels surrounding the translated X,Y address. In the preferred embodiment of the invention, the scan conversion of the X,Y addresses is accomplished in a seven stage scan converter pipeline.

Disclosed is a system for high speed conversion of radar formats from polar coordinates to cartesian coordinates. From an initial address X.sub.i Y.sub.i where a radar pulse crosses a display, subsequent addresses are determined by adding constant values sin .theta..sub.i and cos .theta..sub.i to X.sub.i and Y.sub.i. This is faster than the prior method of calculating x.sub.i and Y.sub.i by multiplying R.sub.i (range) by sin .theta..sub.i and cos .theta..sub.i. Also disclosed is a system for filling the display between adjacent radials at long ranges where spoking of the display tends to occur. This is done by adding constant increments to one cartesian value on one vector until the next vector is reached while maintaining the other cartesian value constant.

Radar data vectors of a desired number of pixels in length are scan converted, at a desired angular rate. A complete 360 degree radar data scan is maintained in memory. A raster image of a desired number of pixels in size and of arbitrary position and angular orientation with respect to the radar scan in memory is outputted. The resolution of the raster output image is varied to adjust its update rate. A high resolution, motion stabilizing radar display is provided and a multiresolution capability is available to eliminate image artifacts attributed to raster image update rate.

A digital scan converter is disclosed wherein signal information supplied by a sector scanning surveillance system relative to a polar coordinate system is converted to a signal for driving a television-type display or other Cartesian coordinate device by: (a) sampling the signal associated with each consecutive scanning path of the surveillance system at a rate determined by the azimuthal angle that defines the scanning path of interest; (b) storing each set of signal samples as a column of data in a rectangular memory array; (c) accessing the stored data on a row-by-row basis; and (d) utilizing a previously determined mapping strategy to cause each accessed signal sample to form a segment of a line of display within the Cartesian-formulated display devices so that the length of the segment formed by each signal sample is determined by the row and column address of the storage location that is associated therewith when forming a television compatible signal, each signal sample dictates video signal level during a portion of a corresponding horizontal sweep period that is determined by the mapping strategy.

Graphics for television display which emphasize circles, ellipses, circular or elliptical arcs, and the radii of circles or ellipses are conveniently stored in image memories addressable in polar coordinates. Television images which are to be rotated are conveniently stored in such memories, so the angular coordinate of the image memory addresses can be incremented or decremented to rotate the image with hardware as simple as a single adder. To read image memories addressed in polar coordinates, the Cartesian coordinates descriptive of television raster display are scan-converted to polar coordinates. This scan conversion takes place in real time at video sampling rates. The generation of the angular coordinate of the polar coordinates is facilitated by dividing one Cartesian coordinate by another by differentially combining their logarithms as found from read-only-memory table look-up, then finding an arc tangent from the logarithm of their difference as found from further read-only-memory table look-up. Since the non-linearities of the logarithm and arc tangent functions tend to track each other to a degree, combining the anti-logarithm and arc tangent look-up steps in a single read-only memory provides greater angular resolution for number of bits used in the read-only-memory input addresses.