Graphics Programs Reference
In-Depth Information
As you might have guessed, the adjective
parametric
is derived from the noun
parameter
(and so endeth today's English lesson). If you look up
parameter
in most dictionaries,
you'll get an explanation in terms of pure math — and that's
waaaay
deeper than you
need to go. For the purposes of making drawings in AutoCAD, think of a
parameter
as a
rule — and therefore think of
parametric drawing
as rule-based drawing.
AutoCAD's parametric rules — officially they're called
constraints
— fall into two cat-
egories:
Dimensional constraints:
Based on dimensioned distances on or between objects
or points on objects. For example, you could apply a dimensional constraint to
two lines that represent a wall thickness so that regardless of where you moved
them or how you rotated them, they would always be 6" or 150 millimeters apart.
Geometric constraints:
Based on object types and relationships between objects;
different object types have different potential constraints. For example, you can
apply a concentric constraint to an arc and a circle so that when you move one, it
maintains its position in relation to the other.
Both AutoCAD and AutoCAD LT support constraints, but as is usually the
case, the feature is limited in LT. If you use the full version, you can create and
modify geometric and dimensional constraints, as I describe in the steps in this
chapter. If you're using LT, you can't
create
either type of restraint, but you can
work with existing constraints in drawings that were created in AutoCAD itself.
Figure 19-1 shows the difference between the AutoCAD and AutoCAD LT Paramet-
ric tabs.
If you're using AutoCAD LT, or if you just want to check out some ready-made
parametric possibilities, you can download the sample drawing datasets from
samples
. The parametric samples are
architectural_example-imperi-
ial.dwg.
,
civil_example-imperial.dwg
, and
mechanical_example-imper-
ial.dwg
.
