The Plotting Area; Unit Systems; The Plotter Unit; User Units - HP 7470A Interfacing And Programming Manual

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The plotting area is that area of the paper in which the pen can draw.
The maximum plotting area for the HP 7470 Plotter is 191 X 272 mm
(7.5 X 10.7 in.) when the paper switch is set to A4, and is 191 X 257 mm
(7.5 X 10.2 in.) when the paper switch is set to us. These plotting areas
permit plotting on either metric A4 size paper or English 8'/2-by-l 1-inch
paper and allow for a margin beween the plotting area and the edges of
the paper.
The plotting area should be thought of as a two-dimensional Cartesian
coordinate system. Remember, in a two-dimensional Cartesian coordi­
nate system, a point is defined by its X- and Y-coordinates; for example,
200,300 represents a distinct point where X = 200 and Y = 300. When
paper is loaded, the orientation of the X- and Y-axes is established as
shown in the following diagram. When looking at the plotter from the
front, the origin is located near the upper-left corner of the paper. From
now on, we will refer to that corner as lower left, since when a plot is
viewed, the minimum point is generally at the lower-left corner of the
plot.
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Unit Systems
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ESTABLISHING BOUNDARIES AND UNITS
There are two unit systems which can be used to define points in the
plotting area: plotter units and user units. Plotter units are always the
same size. The size of a user unit depends on the parameters of the SC
instruction and the settings of the scaling points, PI and P2.
The Plotter Unit
The plotting area is divided into plotter units; one plotter unit equals
0.025 mm. There are approximately 40 plotter units per millimetre, or
approximately 1000 plotter units per inch. One plotter unit is the
smallest move the plotter can make. When the paper switch is set to A4,
the plotting area contains 10 900 plotter units in X and 7650 plotter
units in Y. When the paper switch is set to us, the plotting area
contains 10 300 plotter units in X and 7650 in Y. While the pen can only
plot in the area mentioned above, parameters of plot commands be­
tween —32 768 and 32 767 plotter units are understood by the plotter.
When plotting in plotter units, only integer values are used; parameters
are truncated to integers. Refer to The Plot Absolute Instruction, PA, in
Chapter 3.
At power on, upon front-panel reset, and whenever an IN command is
sent to the plotter, the scaling point PI is set to 250,279 plotter units
and the scaling point P2 is set to 10 250,7479 plotter units. These settings
are independent of the setting of the paper switch.
User Units
The plotting area can also be scaled into user units. This is done with
the scale instruction, SC, which assigns values to the scaling points P I
and P2. A user unit may be almost any size. The parameters of the SC
instruction are truncated to integers between - 3 2 768 and 32 767.
Parameters of plot commands must also be in that range but may be
decimal numbers with fractional parts. Decimal fractions are not trun­
cated; as a matter of fact, you can set the scaling points at 0,0 and 1,1
and all your data can be decimal fractions between 0 and 1. You can
also use the plot relative instruction to plot to a point which, in user
units, is beyond the range ±32 768 as long as its location, expressed a s
plotter units, is in range. Refer to the plot instructions PA and PR in
Chapter 3. You will probably use the SC instruction and user units for
most plots.
Setting t h e Scaling Points
Scaling points PI and P2 can be set programmatically using the input
PI and P2 instruction, IP, as described in a following section. PI a n d
P2 can be set manually using front panel controls
ENTER, PI,
and P2.
ESTABLISHING BOUNDARIES AND UNITS 2-3