GB1362477A - Display raster computer - Google Patents

Abstract

1362477 Cathode-ray tube displays; generating scanning waves SINGER CO 21 March 1972 [1 April 1971] 13113/72 Headings H4T and H3P The beam spot 19 (Fig. 1) of cathode-ray tube 15 is scanned across the screen in such manner that it appears to trace a predetermined path as viewed from eyepoint 11 via beam splitter 17 and spherical mirror 13 at the centre of curvature of which the point 11 is located. Fig. 2 shows a desired, predetermined path comprising a raster each horizontal line 31 of which is an equal angular segment of a line of latitude and must be scanned in equal time intervals. Point 33 is the centre of the display and corresponds to the intersection with the display of the line 35 (Fig. 1) so that every point on the display, the dimensions 37 and 39 being known, may be defined by an azimuthal (horizontal) and elevation (vertical) parameter with reference to the axes of Fig. 1. Thus the voltages (provided by a computer 27) controlling the deflection Vx, Vy are each a function of azimuthal angle (X scan) # and of elevation angle (Y scan) # and are assumed to be represented by the polynomials Vx = K 1 # + K 2 #<SP>2</SP># + higher order terms Vy = K 3 # = + K 4 #<SP>2</SP># + higher order terms Voltages corresponding to # and # may be produced by integrating a constant voltage periodically (e.g. producing normal scan waveforms) in 43, 45 (Fig. 3) and known techniques employed to produce the power terms and the cross multiplied valves which are then combined in scanning amplifiers 55 and 57, the multiplications by the constants K1 ... K4 being provided by the resistors 59 and 61 the values of which are determined by the polynomial coefficients. The latter values may be determined by the "method of least squares" which involves the development of three dimensional ray trace data for a matrix of points (as viewed from position 11) such as the X's of Fig. 2 and then finding the values of #, #, Vx and Vy for each such point and employing a digital computer to evaluate the polynomial coefficients by the method of least squares. Other methods of determining such coefficients are described.