Concept
shadow vanishing point — where it appears
2 essays name this object, across one field. What follows is each of them, and the objects they name alongside it.
A shadow is a second projection
The construction that puts a shadow on the ground is the construction that puts the scene on the picture plane, with the lamp where the eye was. Shadow drawing is taught as a separate set of recipes and it is one operation with the centre moved, which is why the same code draws both.
Where shadows vanish
The shadows of parallel posts under the sun meet at a point, and that point must lie on the horizon. Under a lamp they meet at the lamp's foot instead. Both are checkable in any photograph, and a picture whose shadows fail the check was not lit by anything.
Named alongside it
The objects these essays reach for when they reach for this one.
HorizonVanishing pointForensic geometryLight directionLight footParallel lightPoint lightResidualShadow constructionSolar altitude