The plotting of pollen diagrams has always been a highly individual process, dependent on locally available hardware and software. Because different printers and plotters run from different sets of control sequences, it has not been possible to transport the information needed to plot a pollen diagram except as the data itself or as a finished, camera-ready diagram. In principle, two users with identical hardware and software could exchange a plotter file (as described by Lou Maher in Newsletter 6, July 1991), but in practice this is rarely done.
The PostScript language provides a way to describe any piece of graphics or text in an ASCII file which can be read and interpreted on many printers (especially, but not exclusively, laserprinters). Software packages now often include a PostScript driver which can either send output directly to the printer/plotter, or generate an ASCII file with the commands to generate the work on any output device with a PostScript interpreter. Since a driver is available in many packages, and the interpreter is available in many output devices, the ASCII file provides a useful way to link the two without both being present at the same site. For example, I do not have Generic CADD5, so I cannot print a copy of Lou's Russian sampler diagram from his .DWG file. But if the plotter file had been written in PostScript, I would be able to produce hardcopy on our laserprinter. As an ASCII file, the PostScript file can be easily moved by e-mail, using file compression, as described by Lou, where necessary.
PostScript is probably most readily available in the Apple LaserWriter printers, but can be added to many other printers by purchase of an additional card. The Apple LaserWriter is an excellent laserprinter, and it can be connected to PC-compatibles through a COM port, but it may be necessary to tinker with the wiring to overcome the incompatibility of Apple and IBM (see, for example, Glover 1989).
This note was written using Wordstar, and printed to an ASCII file using the PostScript driver provided. The pollen diagram was generated from an ASCII file produced from the dataset by a QuickBASIC program. Both files were sent to Lou as e-mail, and were printed by him using his printer. Lou does not have the program used to produce the pollen diagram, and would not be able to generate the diagram himself without the data set, which he would need to convert to a format required by his programs. Sending the copy like this is straightforward for me, sparing me the trouble of packing camera-ready copy in a form to survive postal services, while enabling Lou to produce the copy with no extra editing, and on his own printer uniformly with other copy. He does not need to know what software I used to produce the files, and I need no information about his software or hardware, other than this his output device has a PostScript interpreter.
The PostScript language is a 'simple interpretative programming language' (Adobe Systems Incorporated 1990), which describes the appearance of a page, whether text, graphics, or both. Adobe own the copyright in the operators and specification of PostScript, but allow anyone to use them, under certain conditions. A typical file will have a header, such as %!PS-Adobe-2.0, definition of sundry parameters for the page (e.g. font, character size), and definition of operators (to reduce repetition in the body of the page). %%, followed by a keyword, introduces a standard set of 'document structuring conventions'. Operands precede their operators, so (ABC) show prints 'ABC' at the current location. showpage prints the current page and prepares for the next. For graphics, 20 40 lineto is one segment of a 'path', from '0 0' to '20 40' in the current co-ordinates. Text and graphics alike can be moved around on the page, rotated, and scaled. PostScript files are ASCII, so they can be edited using an appropriate editor (e.g. 'EDIT' in DOS 5, or 'non-document' mode of Wordstar), and I do this with text files to include special characters, but there is not too much that can be done with this kind of fiddling. More significant is the possibility of writing PostScript drivers in any programming language, and thus producing output from almost any software that can be printed on any output device with a PostScript interpreter.
Use of PostScript thus has considerable potential for improving the ready portability of pollen diagrams, whether for publication or as part of information exchange.
Adobe Systems Incorporated 1990. PostScript Language Reference Manual. Addison-Wesley Publishing Company, Reading, Massachusetts, 764 pp.
Glover, G. 1989. Running PostScript from MS-DOS. Windcrest Books, 209 pp.
