Since most laser printers can emulate the EPSON / IBM 9-pin standard, it has always been possible to use them with the GPR utility to produce EMME/2 plots. But since this emulation is limited to a resolution of 144x120 dpi (dots per inch), the output does not yield the quality one might expect from a device capable of 300 dpi.
Either as a standard feature or as a separate add-on option, some laser printers can also emulate the HPGL plotter language. In these cases, the GPL utility can be used to output EMME/2 plots using the full 300 dpi resolution. Unfortunately, the HPGL emulation mode tends to work very slowly, at least on the units we have tested so far.
The de-facto standard of laser printer protocols is the Hewlett Packard
HP-PCL language. This protocol is used in the HP's Laserjet line of
printers and is emulated in most other laser printers on the market today.
The printer-plot utility GPR has now been extended for use with HP-PCL
and a new format file HPLJ.FMT, suitable for any laser printer using this
protocol, is included with all new installations. This format provides
superb plots on 8 1/2" x 11" or A4 pages, using full resolution of 300 dpi.
Since the protocol is using the compressed data transmission scheme, a
full page plot on our Brother HL-8PS printer connected to a 10MHz AT clone
requires only between 60 and 90 seconds print time, depending on the
complexity of the plot.
The resolution of 300x300 dpi results in extremely fine lines on the paper,
since normally the lines drawn by GPR are only one pixel wide. This results
in plots that can contain an enormous amount of details. For some
purposes however, as e.g. the preparation of overhead projection slides, these
one-pixel lines are too narrow and thicker lines would be preferable.
For this reason, the new version of GPR also allows the specification
of an arbitrary n-pixel line width. Since this new feature is implemented
not when the vectors are generated but using an aliasing technique when
the plot is completed, it does not affect the efficiency of GPR.
An example format file HPLJ-W2.FMT is provided with the new version of the
program; it defines the same Laserjet format as HPLJ.FMT, but uses a
line width of two pixels instead of one.
As a second standard protocol for laser printers, Adobe's PostScript language
is also rapidly gaining acceptance in this market. Most higher
priced printers, as well as most desktop publishing packages, provide support
for this protocol. We have developed a format description file POSTSCR.FMT for
the GPL utility which generates directly PostScript output. This not
only allows the production of high quality plots on PostScript printers, but
also provides a direct interface between EMME/2 and most desktop publishing
systems, allowing for plots to be inserted into project reports without the
usual "cut and paste". Note that the PostScript interface was done entirely
at the format file level and did not require any changes to the GPL program.
If you need the new version of GPR with Laserjet interface or the PostScript format file for GPL before the next official release, please contact INRO.