Use these terms while testing a sketch in the impossible shape detector. For longer explanations, compare impossible-object vocabulary with the methodology.
Impossible geometry
A drawing suggests individually plausible parts that do not fit a single consistent solid interpretation. The image itself remains an ordinary two-dimensional arrangement of marks.
Perspective paradox
Local perspective cues suggest incompatible global relationships. A contradiction in a picture is not proof that its subject cannot be staged from one viewpoint.
T-junction
One contour ends against another, often suggesting occlusion. In a drawing it is a depth clue, not a measured 3D relationship.
Blivet
An impossible trident whose prongs and connecting beams invite incompatible interpretations. It is also called an impossible fork.
Depth cycle
A sequence of inferred front-behind relationships returns to its starting part with an inconsistent ordering. An ordinary closed outline in a graph is not enough to establish this.
Non-Euclidean geometry
Geometry in which familiar Euclidean assumptions, such as the parallel postulate, do not all hold. An impossible-object illusion does not itself demonstrate non-Euclidean space, and this detector does not analyze curved spaces.