Comment by mnw21cam

Indeed, with hundreds of millions of polygons, a rasterisation method will generally have to splat them all onto the screen one by one (minus some clever occlusion pre-processing). By contrast, a ray-tracer has the ability to shove all the objects into a R-tree or kd-tree, and efficiently search for only those objects that intersect the ray, and produce the objects in guaranteed order of distance from the camera.