Graphics Reference
In-Depth Information
Fig. 4.4
Measurement types
4.2.2
Radial
A radius is the distance from the center of an arc or circle to any point on the arc or
circle. It is often not possible to measure from the physical center of an object to its
surface in order to determine its radius. To determine this measurement on circular
objects, one may instead measure the diameter of a circular object and then divide
the number by 2. A diameter is the length of a straight line that passes through the
center of a circular object and terminates at either end where it intersects the surface
of the object (Fig. 4.4 ). This measurement type is not used in CG, but may be used
to determine radius. Diameter is easily acquired by using a device known as a
caliper or a micrometer . If the circle is too large for calipers, you may be able to
measure the circumference, the distance around the circle, with a tape measure.
To fi nd the radius from the circumference, divide the circumference by pi to get the
diameter, and then divide by 2 to get the radius, like so:
C
p
2 = .
r
4.2.3
Angles
An angular measure is of the deviation of two points from a common location. This
type of measurement is easily accomplished for planar surfaces by using a protractor
or by calculation based on information contained in your target object (Fig. 4.5 ).
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