Elliptical features are described in an image generator database in terms of an origin and major and minor axes defined by reference to a world or model space coordinate system. Image data is assembled for display by transforming the database contents into screen space and assessing for each of an array of sampling points distributed across screen space which features are to contribute to the portion of a final image in which the sampling point is located. In the case of elliptical features, data is transformed into eyepoint space and each sampling point is projected into eyepoint space to determine the point of intersection between a line drawn through the sampling point from the eyepoint and a plans defined by the axes. The coordinates of the intersection point in a coordinate system defined by the origin and axes, are used to determine whether or not the feature contributes to the sampling point.
IMAGE GENERATOR