Graphics Programs Reference
In-Depth Information
Figure 14-2: The parts of a dimension.
Dimension lines: In linear dimensions, the dimension lines indicate the true dis-
tance between points. Linear dimension lines can be horizontal, vertical, rotated
at a specific angle, or aligned with the object being dimensioned. Angular dimen-
sions have curved dimension lines with the center of the curve at the vertex point
of the objects being dimensioned. For radius and diameter dimensions, the dimen-
sion line simply points at the object being dimensioned (see Figure 14-3 for ex-
amples of these dimension types).
Arrowheads: The dimension's arrowheads appear at the end or ends of the dimen-
sion lines and emphasize the extent of the dimensioned length. AutoCAD's default
arrowhead style is the closed, filled type shown in Figure 14-2, but you can choose
other symbols, such as dots or tick marks, to indicate the ends of the dimension
lines. (Don't get ticked off, but AutoCAD calls the line ending an arrowhead even
when, as in the case of a tick mark, it doesn't look like an arrow.)
Figure 14-3: Common types of dimensions.
Extension lines: These extend outward from the definition points (also known as
defpoints ) that you select (usually by snapping to points on an object) to the di-
mension lines. By drafting convention, a small gap usually exists between the def-
points and the beginning of the extension lines. Also by convention, the extension
lines usually extend just past the dimension lines — see Figures 14-2 and 14-3 for
examples. You can make a set of dimensions look tidier by assigning fixed lengths
for the extension lines. And if you need to dimension to circles or centerlines, you
can assign dash-dot linetypes to either or both extension lines.
Defpoints: When you create any kind of dimension, AutoCAD places one or more
definition points (universally known as defpoints ) on a special layer named (what
else?) Defpoints, which the program creates when a dimension command is issued
for the first time. These points are usually invisible because the objects being di-
mensioned are on top of them, but you can see where they sit by selecting a di-
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