Despite their initial appearance of complexity, shadows and reflections obey the same immutable rules of perspective illustrated in the preceding sections of this book.
Shadows are determined by the source of light, the shape of the object, and the surface on which they are cast.
Reflections are simply an extension of the object image onto another plane or set of planes within the perspective view.
The position of the light source is the critical factor in determining the final shape of the shadow cast in perspective, as summarized below and explained further on the following pages.
When the light source is parallel to the picture plane, parallel rays will remain parallel and define the cast shadows according to how they are blocked by the object.
The length and shape of cast shadows are determined by the intersection of the ground plane, with light rays crossing the corners and edges of the object.
Here, the ground plane lines are parallel to the picture plane.