chapter 2 Coordinate Systems

1. Johnson Lim© 2005 All Rights Reserved
Chapter 2
Coordinate Systems in AutoCAD

2. Johnson Lim© 2005 All Rights Reserved
Using Coordinates…
• A good understanding of how co-ordinates
work in AutoCAD is absolutely crucial to
construct drawings more easily.
• Co-ordinates fall into two types, namely
Cartesian and Polar.
• These two co-ordinate types can be either
Absolute or Relative.
• Knowing just when and where to use the
various types of co-ordinate is the key to
efficient drawing with AutoCAD.
Courtesy of CADTutor (2005)

3. Johnson Lim© 2005 All Rights Reserved
Cartesian Co-ordinates
• Named after the French philosopher
and mathematician René Descartes
(1596-1650)
• Standard co-ordinate system
• The position of a point can be described
by its distance from two axes, X and Y.
• This results in a simple point description
using two numbers separated by a
comma e.g. 34.897,45.473.
Courtesy of CADTutor (2005)

4. Johnson Lim© 2005 All Rights Reserved
Examples of Cartesian Co-
ordinates
Courtesy of CADTutor (2005)

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Some extra…
• AutoCAD allows you to use co-ordinates to
draw objects rather than using pick points.
• For example you could draw a line like this:
• This sequence draws a line between the two
co-ordinate points specified.
Command Sequence
Command: LINE
From point: 34.897,45.473
To point: 54.896,65.395
To point: (press enter key to end)
Courtesy of CADTutor (2005)

6. Johnson Lim© 2005 All Rights Reserved
Polar Co-ordinates
• Polar co-ordinates use one distance
and one angle to describe the position
of a point rather than the two distances
in the Cartesian system.
• The distance and angle measurements
are made relative to an origin.
Courtesy of CADTutor (2005)

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Examples
• This results in a point
description which looks like
34.897<30 where the first
figure is the distance (in
drawing units) and the
second is the angle.
• AutoCAD angles start at 3
o'clock (i.e. along the
positive portion of the X axis)
and increase in an anti-
clockwise direction.
Courtesy of CADTutor (2005)

8. Johnson Lim© 2005 All Rights Reserved
The UCS Icon
• This is called the UCS (User
Co-ordinate System) icon
and it is there to remind you
which is the X axis and which
is the Y axis.
• The empty box at the
intersection of the X and Y
axes is there to remind you
that you are using "World"
co-ordinates and that the
UCS icon is not positioned
over the true origin of the
current co-ordinate system
Courtesy of CADTutor (2005)

9. Johnson Lim© 2005 All Rights Reserved
Absolute & Relative Co-ordinates
• Both Cartesian and polar co-ordinates come
in two flavors, absolute and relative.
• The distinction is quite simple, absolute co-
ordinates relate to the X and Y axes and the
origin of the current co-ordinate system,
whilst relative co-ordinates relate to the
current pick point.
• To specify a relative co-ordinate you need to
use the "at" symbol as a prefix.
• "at" symbol = @
Courtesy of CADTutor (2005)

10. Johnson Lim© 2005 All Rights Reserved
Examples…
• Relative co-ordinates are very useful for
drawing objects which you know the size of.
• For example, you could draw a square of 12
units with its lower left hand point at 30,40 as
follows:
Command Sequence
Command: LINE
From point: 30,40 (an absolute Cartesian co-ordinate)
To point: @0,12 (a relative Cartesian co-ordinate)
To point: @12<0(a relative polar co-ordinate)
To point: @0,-12 (another relative Cartesian co-ordinate)
To point: C (to close)
Courtesy of CADTutor (2005)

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More Examples
• You can also use this method to quickly draw
a rectangle of known size.
• Say you needed to draw a rectangle 20
drawing units wide and 10 drawing units high
and you didn't mind where exactly the
rectangle is drawn, you could do this:
Command Sequence
Command: RECTANGLE
Specify first corner point or
[Chamfer/Elevation/Fillet/Thickness/Width]:
(pick a point near the middle of the drawing area)
Specify other corner point or [Dimensions]: @20,10
Courtesy of CADTutor (2005)

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Display Controls
• Display controls enables users to have
easier viewing of their drawings.
• These includes zooming and panning of
drawings.
• The commands include zoom, pan,
redraw, regen, aerial view etc.

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The Zoom Commands
• Zoom Window : Select a window over the
location to zoom into. AutoCAD will zoom in close
to the object including everything within the
selection box.
• Zoom Dynamic : Enables the user to set the size
of a standard zoom window type box, then use
this box to select zoom in views of the drawing
with this box with clicks of the mouse button.
Courtesy of AutoCADCentral.com (2005)

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Zoom  Windows…
Courtesy of AutoCADCentral.com (2005)

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The zoom continues…
• Zoom Scale : Enables the user to zoom into the
drawing to a known scale
• The value you enter is relative to the limits of the
drawing. For example, entering 2 doubles the apparent
display size of any objects from what it would be
• If you enter a value followed by x, AutoCAD specifies
the scale relative to the current view. For example,
entering .5x causes each object to be displayed at half
its current size on the screen.
• If you enter a value followed by xp, AutoCAD specifies
the scale relative to paper space units. For example,
entering .5xp displays model space at half the scale of
paper space units.

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Zoom Command
• Zoom Centre : Specify a centre point, then a
radius and AutoCAD will centre this view to fit
your screen.
• Zoom In : zooms into the drawing slightly
• Zoom Out : zoom out of the drawing slightly
• Zoom All : Zooms to the extents of the
drawing limits. Don't worry about this just yet.

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The Zoom Command
• Zoom Extent : One press will zoom to the extent of
the entire drawing enabling a very quick overview of
the project and an easy starting point to zoom into a
more precise area of the drawing with one of the
above tools.
• Zoom Realtime : will zoom in and out of the drawing
dependant on how far you move your mouse. Left
click and hold the left mouse button down. AutoCAD
will zoom in further into the drawing the further you
move you mouse up (away from you). Try pulling the
mouse down with the left button still held down,
AutoCAD will zoom out.

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Panning…
• Concept: moving your drawing paper by
hand
• Drawings are neither zoomed nor
scaled.
• Pan  Point : Require point to put and
place
• Realtime Pan : Can pan in real-time by
holding mouse clicks.

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Other Display Controls…
• REDRAW/REDRAWALL: redraws the current
viewport, removing marker blips and display
artifacts (stray pixels) left by editing commands.
REDRAWALL did the same thing in all viewports
• REGEN/REGENALL: REGEN regenerates the
entire drawing and recalculate the screen
coordinates for all objects. It also reindexes the
drawing database for optimum display and object
selection performance.
• REGENAUTO: drawings regenerate automatically.
If you are working on a large drawing, you may
want to set REGENAUTO to off to save time.

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One last command…
• VIEWRES: controls the appearance of
circles, arcs, ellipses, and splines using
short vectors. The greater the number
of vectors, the smoother the
appearance of the circle or arc.
• For example, if you create a very small
circle and then zoom in, it might appear
as a polygon. Regenerating the drawing
updates and smoothen the circle's
appearance.