The Hewlett Packard Graphic Language ( HP -GL) is a technology developed by Hewlett -Packard page description language for driving pen plotters. Other plotter manufacturers have adopted the language of HP -GL plotter to control their own.

Language structure

HP -GL is a language of simple construction. The commands consist of two uppercase letters, which followed by one or more arguments. The transmission of data is done in "clear text" (ASCII).

The coordinate system is based on the smallest unit that supported an HP plotter then and was set to 25 microns ( 40 units per millimeter or 1016 units per inch).

Inkjet and laser plotters

Also for the control of inkjet and laser plotters, HP -GL is used. These plotters build the first image in memory ( this is known as rasterization ) and then give it out on paper. Here, this plotter work with " virtual pins " that is, there is a table in which each pin number is assigned to a line width and optionally a color. This table can be stored permanently in the plotter ( now little more common) or be sent along with the HP -GL data ( from HP -GL / 2 or with vendor-specific headers ).

HP -GL / 2

HP -GL / 2 is a further development of the language HP -GL. An important new feature is the ability to set line widths (and other line attributes ) as well as binary and thus space-saving coded instructions to produce (eg PE = Polyline Encoding). Since HP -GL is designed for pen plotters, there was no commands to define the line widths, as these were defined by the pins. The user had to assemble according to his wishes, the Stiftkarussel. When the first inkjet plotters came up, the user had instead on a plotter pen table to enter. With HP- GL / 2 of this uncomfortable and error-prone step was unnecessary.

HP-GL and HP-GL / 2 as data exchange format

Although it was not designed to be HP- GL developed because of its simplicity for data exchange format for vector data graphics. Many CAD programs allow you to export in HP-GL format. Another common option, HP- GL data to produce the "Print to file " with an appropriate printer driver. This is problematic, since the language is extended again and again with the release of new chartplotter and it could lead to compatibility problems. Another problem is vendor-specific headers that are sent before the actual HP-GL data in order to drive certain Plottereigenschaften - for example, the Printer Job Language of Hewlett -Packard or the remote control format of Océ.

( Free after Jonathan Postel ) For the avoidance of compatibility issues: be liberal in what you accept, be conservative in what you send. One can assume that the instruction set of the plotter HP750C is generally understood. In addition, the software technically very limited systemic accuracy of a " pressure " in this simple transmission format to be considered against the DXF file format.

HPGL is also used for controlling engraving machines.