Patent GB-1453097-A (GB)
Title: Display of a digitally stored image on a spherical viewing surface
IPC: G01S7/22
Filed: 1973-12-31
Abstract: 1453097 Cathode-ray tube displays SINGER CO 31 Dec 1973 [22 Jan 1973] 60272/73 Heading H4T  Display apparatus employs a cathode-ray display tube the screen of which forms part of a sphere over which the beam spot is deflected at a constant scan rate to form raster lines which lie on great circles, digital means determines the position of the point of intersection with a simulated plane tangential to the screen of a line of sight passing from a viewpoint position through the instantaneous position of the scanning spot and a digital image signal generator responsive to output signals from the digital means generates video signals which are supplied to the cathode-ray tube. The image is deemed to be produced in a planar image surface 12 (Fig. 1) and to be formed by image points lying on parallel lines 14, 14a &c. line 14 being tangential to the spherical viewing surface 8 at point 9. The centre of curvature of 8 is indicated at 11, 10 is the radius r and 15 represents a line of sight from an eyepoint at the centre 1. Thus an image point such as 16 on line 14a is viewed at position 18, the display point and as the line of sight successively passes through the surface 8 to each of the image points on each of the lines 14, 14a &c. the intersected display points define a family of great circles 19 (Fig. 2) intersecting at polar points 20, 21. Fig. 3, shows a part of the spherical surface 8 together with an equatorial plane 22 including radii 24 and 26, the latter being also included in a central vertical plane 28 which is perpendicular to the image surface 12 and to plane 22. Additionally, a slant plane 30 is shown which is perpendicular to plane 28 and includes image line 14a and the radius 24. Figs. 3a to 3d show, respectively, plan views, of the central vertical plane 28, the slant plane 30, the image surface 12 and the equatorial plane 22 including the elevation angle 34 (Fig. 3a)=# and the azimuthal angle 46 (Fig. 3d) = α. Fig. 4, shows the described embodiment and includes a counter 48 supplied with clock pulses and providing, on lines 51, a constant rate digital displacement output (for raster line deflection) and on line 54 a pulse output when the end of a raster line is indicated, this pulse resetting counter 48 and providing a line count to a second counter 52. The output of the latter is supplied to a R.O.M. (Read Only Memory) 56 comprising a decoding apparatus such as a diode matrix constructed to operate on its input in accordance with the indicated function to provide an output comprising a digital signal representative of the elevation angle # which is supplied via D/A converter 62 to the elevation control input of the display means 64. The output of circuit 56 is also supplied to a second R.O.M. 68 similar to R.O.M. 56 which also receives the count signals on lines 51 and operates in accordance with the indicated function to provide an output comprising a digital signal representative of azimuth angle α which is supplied via D/A converter 70 to the azimuth control input of the display means 64. Additionally, the output # of R.O.M. 56 and the signals on line 51 are supplied to a third R.O.M. 76 operating according to the indicated function and supplying an output X (see also Fig. 3b) comprising a digital signal representation of the displacement of an image point along an image line. This output together with the output of counter 52 are supplied to the digital image generator which in response to concurrence of the two inputs provides a signal output controlling the display of the image by display means 64.