GB1520452A - Electronic curved surfache simulator - Google Patents

Abstract

1520452 Curved surface simulators GENERAL ELECTRIC CO 23 July 1975 [7 Aug 1974] 30845/75 Heading G4A [Also in Division H4] A method is described for producing from a store of environmental date defining objects on a curved surface, such as the earth, in terms of orthogonal curved co-ordinates on the curved surface and elevations measured normal to the curved surface, a two-dimensional visual perspective presentation of such objects as would be viewed from a viewpoint elevated above the curved surface, the method being carried out by data processing means. The method involves calculating the squares of the ranges, r<SP>2</SP>, on the curved surface, of the curved surface positions of points in the defined objects from the projection of the viewpoint on the curved surface. It is shown that, in order tha the presented points shall be in correct elevational relationship, an elevation correction given to a good approximation by r<SP>2</SP>/2E, where E is the radius of curvature of the curved surface, must be subtracted from the elevation of the corresponding point in a defined object, when the curved surface is replaced by a plane tangential to the point of projection of the viewpoint on the curved surface. A plane is used instead of the actual curved surface to shorten computation time. Objects are transferred from the curved surface to the plane by measuring the curved surface co-ordinates of each point in an object and transferring the measured coordinates to orthogonal straight axes in the plane, the corrected elevations also being transferred. Intersections of lines from the viewpoint to the points so obtained with a view window plane (a view window being a rectangular area viewed through in order to select a desired portion of the curved surface) are then calculated, the intersections being displayed on, e.g. a cathode ray tube display device to produce the perspective presentation. Corrected elevations of points on the horizon, at range R, are also calculated by the formula R<SP>2</SP>/2E and the corrected horizon displayed. The environmental data may carry associated priority information to determine which of two objects of different ranges hides or is hidden by the other perspective presentation, or to determine whether earth or sky should appear instead of an object, e.g. in the case of an object below the horizon. For an object further away than the horizon and partially below the horizon, the part below the horizon is suppressed from presentation. The environmental data may also contain information on any plane areas defining an object, e.g. in the form of unit normal vector to a plane area, in order that it may be determined whether a plane area faces the viewpoint and is thus visible, or the reverse. Colour information may also be associated with the environmental data in the case of a colour display device being used.