Inclined plane — where it appears
Named by 2 essays across one field — each of them below, with the objects they name alongside it.
The ramp has its own horizon
Every plane has a vanishing line, and a ramp's is not the ground's. Its uphill edges meet on a line above the horizon, and the angle at the eye between that meeting point and the same direction taken level is the gradient — 22.0000° recovered against 22° built, out of the picture alone, with no scale, no ruler and nothing known about the scene except that the ground is level.
The line every nosing is on
Nothing in a staircase points up the pitch. Every surface in it is level or vertical, and its picture has a vanishing point off the horizon all the same — belonging to the line the front edges of the treads lie on. That point is not free: it is collinear with the travel point and the vertical point, and the angle it makes says the rise-to-run the builder chose.
Named alongside it
The objects these essays reach for when they reach for this one.
Focal lengthHorizonsingle-view metrologyVanishing pointAngle from vanishing pointsCollinearityForeshorteningGradientIncidenceOrthocentrePicture planepoint at infinity