Validation of CG Models - An Introduction to Computer Graphics for Artists - page 115

Fig. 9.1 The yellow curve is controlled by control vertices, shown as purple circles . When a line
drawn through each control vertex bisects the curve, that is the infl ection point (in orange ), the
point where the curves changes direction

Fig. 9.2 The vertices of polyline a are evenly distributed. This causes them to miss detail in the
tight corner on the right . In polyline b , vertices are distributed based on curvature. This allows for
a more natural curve at the expense of some shallow detail

the tight part of the curve if the resolution of the model is too low. If the resolution
is high enough to capture the smaller curve, it might be too high for the rest of the
curve. For objects like this, it is best to place vertices at the apex of every curve sec-
tion and at any infl ections . An infl ection is a point where the curve inverts its direc-
tion, as in the center of an “S” curve (Fig. 9.1 ).
For higher resolution, edges should be divided evenly between existing points. In
this way the details of the curve are captured without sacrifi cing smoothness (Fig. 9.2 ).

9.2.2 Distortion

Some objects have connections that result in distortion if one of the connected ele-
ments is moved but another is not (Fig. 9.3 ). This happens because the application
does not treat polygons as real world objects unless those properties have been