dx = ddx(WorldPosition.x)
dy = ddy(WorldPosition.y)
dz/dx = ddx(height) / dx
dz/dy = ddy(height) / dy

let Tan(theta) = dz / dx
let Tan(phi) = dz / dy

sin(phi)
-sin(theta)cos(phi)
cos(theta)cos(phi)

TopLeft = Texture[uv + (-small, -small)]
TopRight = Texture[uv + (small, -small)] + (2.0 * small * world unit converter, 0, 0)
BottomLeft = Texture[uv + (-small, small)] + (0, 2.0 * small * world unit converter, 0)

v1 = TopRight - TopLeft
v2 = BottomLeft - TopLeft

n = cross(v1, v2)