Hp-Gl (Hewlett-Packard Graphics Language); The Plotter Coordinate System; Plotter Units; Plotting Limits - HP 7470A Operator's Manual

HP-GL (Hewlett-Packard Graphics Language)

HP-GL is the graphics programming language that is actually sent to
and understood by the 7470A plotter. HP-GL commands consist of two­
letter mnemonics that are usually followed by numeric parameters.
With the exception of certain escape sequence commands which are
used for control of interface functions in an RS-232-C/CCITI' V.24
environment, all data received by the plotter is interpreted as HP-GL
commands. You can include HP-GL commands directly in the computer
language output statements, or you can use BASIC graphics statements
which the computer encodes and sends to the plotter as HP-GL com­
mands. The HP 7470A Interfacing and Programming Manual contains
complete information about handshaking and programming in HP-GL.
T he Plotter Coordinate System
The plotting area should be thought of as a Cartesian coordinate
system with both the X- and V-axes scaled into plotter units. The
location of the coordinate origin (0,0 plotter units) and the orientation
of the X- and V-axes are shown in the following diagram. Plotting
limits and the default locations of P l and P2 are also shown.

Plotter Units

A plotter unit is 0.025 mm (approximately 0.001 in.) in length and is the
smallest move the plotter can make. The numeric range of plotter units
is -32 768 to + 3 2 767, and is far greater than the limits of the paper
which can be used with the plotter. When the plotter is commanded to
plot data which is within the above range but beyond the limits of the
paper, it plots to the plotting limits, monitors the location of the off­
scale data points, and resumes plotting when the data again represents
points on the paper. The graphics position is defined to be this moni­
tored position regardless of whether it is on or off the paper.

Plotting Limits

Plotting limits determine the maximum limits of the pen's motion and
the area within which Pl and P2 can be positioned. The plotting limits
are determined by the position of the
plotting limits establish a rectangular plotting area with a range of 0 to
10 900 plotter units in the X-axis and 0 to 7650 plotter units in the Y­
axis. In the
us
plotter units in the X-axis and 0 to 7650 plotter units in the Y-axis.

The Scaling Points PI and P2

On power-up, scaling points Pl and P2 are set to the coordinates P h
250, P l y 279, P2x
= =
22
position, plotting limits are in the range of 0 to 10 300
1 0 250, and P2y
=
switch. In the
A4/us
7479 plotter units. These
=
position,
A4