Object-based irregular-grid volume rendering

Method and apparatus for rendering data for display. The data represents a model space and the method includes the following steps. A first step associates individual points in the model space with individual vertices (V) of an irregular grid cell enclosed by faces. Each of the points has an associated luminosity value and an associated opacity value. A next step orders the faces of the grid cells. The faces are preferably ordered by depth referenced to a view plane. A further step processes individual faces for determining, for all viewing rays that project from pixels on the view plane and that intersect the face being processed, an amount of light arriving at the pixel. The amount of light arriving at the pixel is a function of both the luminosity and the opacity of a grid cell that lies adjacent to the face and through which the viewing ray passes.