Game Development Reference
In-Depth Information
Table 14.2 Units of Measurement
Physical Description
of Smallest Representable
Object (as a Textured
Polygon)
Smallest
Unit
Upper Range
in Meters
Physical Description of
Area in the Upper Range
A group of redwood trees 1.67 × 10
9
100m
Earth/Moon System
1.67 × 10
7
1m
A human being
North and South America
1.67 × 10
6
1cm
A coin
California
1.67 × 10
5
1mm
A flea
San Francisco Bay Area
1.67 × 10
4
100 μm
A grain of pollen
Downtown San Francisco
design. Most games can safely use the 100 micrometer (μm) basis since your sandbox
can be as big as downtown San Francisco. The human eye can barely detect objects
100μm across but can
t discern any detail.
This is why most games set their basic unit of measurement as the meter, constrain
the precision to 1mm, and set their maximum range to 100 kilometers. Most art
packages like 3ds Max enable artists to set their basic unit of measurement. If you
use such a package, you need to make sure they set it to the right value for your
game.
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Agree with Your Artists on a Standard Unit of Measurement
A common source of problems in computer game development is when artists
and programmers can
t seem to get their units of measurement correct. Game
objects and game logic might use different units of measurement, such as feet
instead of meters. One clue: If things in your game appear either three times
too big or
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three times too small,
someone screwed up the units of
measurement.
Now that we
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ve nailed the range and precision of the 3D coordinates, let
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s take a few
moments to consider those arbitrary decisions about origin and axes directions.
You
ve probably heard of 3D coordinate systems described as either left- or right-
handed, and if you
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re like me, you tend to forget which is which, and the explanation
with your fingers and thumbs was always just a little confusing because I couldn
'
t
remember how to hold my hands! Here
'
s another way to visualize it. Imagine that
you are standing at the origin of a classic 3D Cartesian coordinate system, and you
are looking along the positive X-axis. The positive Y-axis points straight up. If the
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