Traditional Whitted-style ray tracing is done with intersection tests, that is, the scene is rendered by testing if rays coming out of the camera and going into the scene intersect with various objects. With this style of rendering, in order to be able to render a 3D object, you need to be able to write a piece of code that checks whether or not a given ray intersects with the object, and if so, where the nearest intersection occurs (there might be multiple). The technique, known as ray marching, or sphere tracing, makes it possible to render a scene that is directly defined by a Signed Distance Function (SDF).