Measurements and Their Relationship to CG - An Introduction to Computer Graphics for Artists - page 48

Chapter 4
Measurements and Their Relationship to CG

4.1 Introduction

In CG, everything is measured. Polygons are made of vertices whose locations are
measured from the global origin along coordinate axes that provide orientation.
Pixels in texture maps have XY coordinates as well as colors that are measured
amounts of red, green, and blue. Lights are located based on measurements; their
intensity is a measurement, as are all of their other variables. Transformations are
measurements of the difference between one position and another. All things in a
CG environment rely on measurements for their depiction.
Modeling then, is measuring. The quality of the measurements used in a CG
scene will determine the quality of the scene itself. Ask yourself this: what is the
difference between two millimetres and three? In the context of this discussion, the
difference is 150 %. Imagine what that means. Robert Pershing Wadlow, the tallest
man to have had his height authenticated was 8 ft 11.1 in. tall (2.72 m) at his death
(Herder 2009 ). At this height, he was 150 % taller than someone who was 5

(1.81 m) (Fig. 4.1 ). The difference between these two measurements is striking.
Despite the enormous difference that an additional 50 % makes, artists with weak
visuo-spatial skills frequently make this magnitude of error. Art instruction alone
is not enough to overcome a tendency to mismeasure things (Haanstra 1996 ), but
practice devoted to increasing one's sensitivity to measurements can help.
In the carton exercise, you didn't have to worry about measurements unless you
made a drawing instead of scanning the carton. When the carton was scanned,
the scanner used a consistent pixel to linear dimension ratio, known as dots per
inch , or DPI (Fig. 4.2 ). This caused the exact dimensions of your scanned carton to
become embedded in the resulting image. If it was scanned at 150 dpi, and one edge
was 750 pixels in length, then that edge is 5 in long because 750
150

′ 11 ″

. In some ways,
modeling is all about measurements, and without them, there would be no such
thing as 3D graphics.

= 5