Computer Studies 9: Design, Drawing & CAD 1
Sands Secondary
Precision Input
There are several tools available in AutoCAD to assist in the creation of precise drawings:
SNAP –
Controls cursor movement to increments specified. Good for simple drawings
where measurements are whole numbers. Often used with GRID (a visual reference).
ORTHO –
limits the cursor to draw in only vertical or horizontal movement.
POLAR Polar tracking restricts cursor movement to specified angles. This can be used in
conjunction with the keyboard to produce lines of a specific length at a polar angle. For example,
if POLAR was set to 45, an alignment path and tooltip are displayed when your cursor crosses
the 0 or 45-degree angle. The alignment path and tooltip disappear when you move the cursor
away from the angle. To create a line exactly 5.2 units long at an angle of 45, you would set the
cursor in the direction you want to go (as shown), and then type 5.2 on the keyboard.
Note: Ortho mode and polar tracking cannot be on at the same time. Turning on polar tracking
turns off Ortho mode.
OSNAP
All entities in AutoCAD have snappable reference points – for example, you may
snap to a line’s endpoint, its midpoint, or its other endpoint. If the line crosses another entity, you
may also snap to the intersection of the two entities.
TRACKING
Tracking is used in conjuction with object snaps (OSNAP) to define a point
based on reference points. For example, the centre of a rectangle may be found by tracking the
midpoints as shown below
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Computer Studies 9: Design, Drawing & CAD 1
Sands Secondary
ABSOLUTE AND RELATIVE KEYBOARD INPUT
The AutoCAD drawing environment is based on a Cartesian coordinate system. Any point may
be specified by simply keying in the X,Y coordinates while in a drawing command. For example,
in the illustration below, the line could have been created by keying in LINE [Enter] 2,1 [Enter]
5,2 [Enter] (absolute coordinates). The last input could also have been specified as @3,1 [Enter]
(relative coordinates) as this is the relative distance from the last point entered.
Note: when using Dynamic Input
, the @ sign is not required, it assumes relative input.
FROM – is an older keyboard command which is used to Locate a point offset from a reference
point. For example, the centre of a circle is 2 units from the end of a line. Rather than drawing a
construction line, the FROM command could be used, as shown here:
Command: CIRCLE Specify center point for circle or [3P/2P/Ttr (tan tan radius)]: FROM
(snap to the endpoint of the line)
Base point: <Offset>: @2,0
Specify radius of circle or [Diameter] <0.5892>:
The centre of the circle is exactly 2 units away from the endpoint of the line.
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