402 Machine Drawing
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d:\N-Design\Des21-1.pm5
Fig. 21.3 (a) Invoking the ELLIPSE 21.3 (b) The Draw toolbar
The layering concept is similar to the transparent overlays used in many draughting
applications. This allows the user to view and plot-related aspects of a drawing separately or in
any combination. In drawing insertion, a drawing can be stored in a drawing file and this may
be inserted in subsequent drawings for any number of copies. To refer to geometric features of
existing objects when entering points, the object snap may be used. The visual image of the
drawing on the screen may be magnified or shrunk by zooming. Whereas, panning allows viewing
different portions of the drawing, without changing the magnification. In plan view, the
construction plane of the current user co-ordinate system is parallel to the screen. The drawing
may also be viewed from any point in space (even from inside an object). The graphics area of
the screen can be divided into several view ports, each displaying a different view of the drawing.
Physical resolution refers to the amount of detail that can be represented. This resolution can
be changed at any time. The editing facilities of AutoCAD make it easy to correct or revise a
drawing. Multiple copies of an object, arranged in rectangular or circular patterns are easy to
create.
21.7 PLANNING FOR A DRAWING
While planning a drawing in Auto CAD, one has to organize some of the information such as
choosing the units, co-ordinates, etc.
21.7.1 Co-ordinate System
The system used by all the CAD packages is generally the rectangular cartesian co-ordinate
system designated as x, y and z axes. The positive direction of these axes follows the right hand
rule. Any point in space can therefore be designated by the co-ordinate values of these 3 axes.
viz., x, y and z.
