Validation of CG Models - An Introduction to Computer Graphics for Artists - page 114

9.2 Likeness Errors

Likeness errors affect the quality of the likeness in some way. If your object is
measured well, you shouldn't have any likeness errors at all. However, they do
creep in sometimes, so this short list provides a way of fi nding some of the less
easily spotted types of likeness errors.

9.2.1 Relationships

Some likeness errors are not errors on their own but only in combination with
something else. This can be described as a relationship error. A relationship error
is when two things in an object or some quality of two or more different objects do
not match when they should.

9.2.1.1 Scale

A scale error occurs when nearby objects are built to a different scale. This can happen
when different artists work to a different scale or ignore scale specifi cations in their
technical guidelines. When objects built to different scales are imported into the same
scene, the difference can be strong. One bicycle might be 150 cm long, another is
150 m long because the two artists had their units set differently. Units are the mea-
surement type used in a scene, like inches, feet, centimeters, meters, or kilometers.
With characters, scale errors can be just as obvious, but they can also be more
subtle if the artists are working to the same scale, but are not careful about the size
of the characters they are building. Because character modeling is a more organic
process than building mechanical or architectural subjects, it is easy to become
distracted and increase or decrease the size of a character unintentionally. This can
lead to errors in the 50 % range.
The way to avoid this kind of mistake is to check the scale of your scene before
you start. With characters, it helps to create a bounding box that matches the size of
your character. A bounding box is a cube that has been scaled to match the largest
dimensions of your object in the X, Y, and Z axes. For team projects, the bounding
box can be distributed to all the artists on the team. This way, all of their work will
have the correct scale.

9.2.1.2 Curve Fidelity

It is possible to place the vertices of a polygon along a curve in such a way that it is
a poor likeness of the curve. The curve fi delity is the degree to which the vertices of
an object follow the curves they are meant to represent. If a curve starts as a long
gentle curve, then suddenly makes a tight turn, evenly spaced vertices would skip