x' = x + APosition is changed. Orientation and distance are fixed.
y' = y + B
x' = x cos(w) - y sin(w) + APosition and orientation in plane perpendicular to line of sight are fixed.
y' = x sin(w) + y cos(w) + B
x' = AxOrientation is fixed. Distance varies.
y' = Ay
x' = Ax - By + CSurface plane remains normal to line of sight.
y' = Bx + Ay + D
x' = Ax + By + C
y' = Dx + Ey + F
(AE - BD > 0).
3-D motion. Distance from eye to surface is large, so distance to all parts of
surface is essentially the same.
Invariants: Parallel lines. Ratios between distances on parallel lines.
Any parallelogram can be mapped to any other parallelogram.
x' = (Ax +By +C) / (Gx + Hy + I)3-D motion. Surface is close to eye, so some parts are much closer than others.
y' = (Dx +Ey +F) / (Gx + Hy + I)
not(G=H=I=0) and AE-BD != 0.