Validation of CG Models - An Introduction to Computer Graphics for Artists - page 132

Fig. 9.21 A zero edge-length face can be selected, but will not be visible as more than a single
highlighted pixel

temporary modifi cations with the intention of removing them later. If they aren't
removed, then they are construction errors. Because of the complexity of some
models, these can be very diffi cult to fi nd unless you make an effort to remain aware
of the temporary modifi cations you make while modeling.

9.4.2 Coincident Faces

A coincident face is when the vertices belonging to two or more faces have the
same coordinates as each other (Fig. 9.22 ). A partially coincident face is when
part of a face is coincident with another. Both types of coincident faces cause
fl ickering when rendering as the renderer tries to determine which face is in front
of the other.
There are a number of ways to create coincident faces, such as the use of polygo-
nal extrusion tools, then cancelling the operation after the extrusion is made but
before the new faces have been moved into position. Another method is to duplicate
an object without moving it to a new location. This can happen when the object
copy function is mapped to a hot key and it is accidentally pressed.
Coincident faces may be found when there is fl icker during camera rotation in
shaded mode. Another indication of coincident faces is when you attempt to edit a
face, but you cannot. This is because the face you select is not connected to the
object you are trying to edit.