Graphics Programs Reference
In-Depth Information
A button that looks lit (that is, just a little brighter than its neighbors — typically, a
light blue) indicates that the feature is on.
A button that looks dimmed (typically, dark gray) indicates that the feature is off.
Keyboard capers: Coordinate input
The most direct way to enter points precisely is to type numbers at the keyboard.
AutoCAD uses these keyboard coordinate entry formats:
Absolute Cartesian (X,Y) coordinates in the form
X,Y
(for example,
7,4
)
Relative X,Y coordinates in the form @
X,Y
(for example,
@3,2
)
Relative polar coordinates in the form @
distance
<
angle
(for example,
@6<45
)
Understanding AutoCAD's coordinate systems
AutoCAD stores locational data for every object in a drawing based on a centuries-old
system of Cartesian, or X,Y coordinates.
Cartesian coordinates are named for French philosopher René “I think, therefore I am”
Descartes. In his
Discourse on Method,
Descartes came up with the idea of locating any
point on a planar surface by measuring its distance from the intersection of a pair of
axes (that's
axes
as in more than one axis, not the tool for chopping wood). By conven-
tion, the intersection of those axes (called, also by convention, the X-axis and the Y-axis)
are perpendicular to one another, and their intersection point is identified as 0,0. The lo-
gical next step in this system of X,Y coordinates is to introduce a third axis (called, what
else, the Z-axis), perpendicular to the plane defined by the X- and Y-axes. This one
shares the X,Y intersection point of 0,0 and so its coordinates are identified as 0,0,0.
Theoretically, any point in three-dimensional space can be located by a set of X,Y,Z co-
ordinates. And, by extension, every point in an AutoCAD drawing file can be identified
by its X,Y,Z coordinates (in most 2D drawings, the Z-coordinate is 0). This system of co-
ordinates is referred to in AutoCAD as the
World Coordinate System,
or WCS.
Introducing User Coordinate Systems
Many times, it's convenient to define additional coordinate systems to make drawing
things a little easier, so AutoCAD lets you roll your own. These non-World Coordinate
