The Circle Instruction, Ci - HP 7470A Interfacing And Programming Manual

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The Circle Instruction, CI
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The circle instruction, CI, provides the means to draw a
circle of a specified radius and chord angle. It is only included in the
instruction set of RS-232-C plotters that have the serial prefix number
2308A or higher.
The instruction can be used to generate circles with a single
command. All computations are internal to the plotter to reduce com­
puter overhead.
CI radius (, chord angle) terminator
180°
CIRCLE
STARTING POINT:
RADIUS -
CIRCLE
STARTING POINT:
RADIUS +
CURRENT PEN POSITION
270°
The radius parameter can be a positive or negative
number in integer format. Its sign defines the starting point of the
circle: a circle with a positive radius starts at the 0-degree point; a circle
with a negative radius starts at the 180-degree point. The current pen
position is the center of the circle. If scaling is off, the radius is in
plotter units. If scaling is on, the radius is in user units. If user units
are not the same size in the X- and Y-directions, ellipses will be drawn.
The chord angle parameter is in integer format and governs the
smoothness of the circle. It is interpreted as degrees and sets the
maximum angle subtended by a chord that is drawn to represent an
arc segment of the circle, as shown below. The actual angle used may
be changed by the plotter so that all chords are the same length. The
sign of the parameter is ignored, except to set the maximum in-range
limit to - 3 2 768 or +32 767.
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CONTROLLING THE PEN AND PLOTTING
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DESIRED CIRCLE
CHORD ANGLE
The most useful chord angle values range from 0 to 180; where 0
produces the smoothest circle and larger numbers progressively reduce
the number of chords used. Values from 180 to 360 work just the
opposite; i.e., larger numbers progressively increase the number of
chords used and 360 produces the smoothest circle. This pattern follows
modulo 360 through the permitted range of - 3 2 768 to - 3 2 767. Specify­
ing out-of-range parameters sets error 3 and the command is ignored.
The following strings of HP-GL instructions, when sent to the plotter
using your computer's output statements, show the effect of different
chord angles.
" I N ; S P 1 ; I P 2 G 5 0 , 1 3 2 5 , 7 6 5 0 , 6 3 2 5 ; "
" S C - 1 0 0 , 1 0 0 , - 1 0 0 , 1 0 0 ; "
" P R - 5 0 , 4 0 ; C I 3 0 , 4 5 ; "
" P H 5 0 , 4 0 ; C I 3 0 , 3 0 ; "
" P f l - 5 0 , - 4 0 ; C I 3 0 , 1 5 ; "
" P H 5 0 , - 4 0 ; C I 3 0 , 5 ; "
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CONTROLLING THE PEN AND PLOTTING 3-13