Buyer's Guides


Publication Details:
Publication:“PC Plus”, UK
Date:October 1993

Buyer’s Guides: Plotters

Not long ago, buying a hard-copy device for Computer Aided Design (CAD) was easy. The only choice most people had to make was paper size – the use of pen plotting as the core technology was seldom in question. However, the well-ordered universe of CAD hard copy has recently been turned upside down by the arrival of technologies which are normally associated with printing.

A short look at the history of plotters helps us to understand the implications of what’s happening at present. Plotters and printers came from the need to generate two very different types of hard copy namely large line-drawings for CAD and scientific applications, and lines of text characters for word-processing and other popular business programs.

Pen plotters were developed to cater for line drawing, the vector-based operations of this type of device being easy to derive from CAD data. Hewlett Packard’s HP-GL (Hewlett-Packard Graphics Language) plotter language quickly became established as a standard, even to the point where other manufacturers of plotters began to emulate it. Robust and able to generate high-quality output even on large paper sizes, pen plotters could also provide different colours or line-weights simply by swapping pens.

When printers evolved to form lines of text characters from small dots rather than metal type, it quickly became apparent that the technology also had the ability to generate full-page graphics. Although the quality was indifferent and the paper sizes were too small for CAD, the flexibility and low cost of printers meant that more and more users became interested in using them to print the sort of data which was normally sent to traditional pen plotters.

Against this background, several simultaneous developments appear to have triggered off the current level of activity in CAD output. Firstly, the rapid growth in CAD has highlighted a number of long-standing problems associated with pen plotters, particularly when used in a networked environment.

Noisy and messy, output quality is liable to suffer without the correct combination of plotter settings and pen and paper types. More importantly, pen plotters require frequent attention to load fresh pens and paper, and are unsuitable for high-throughput applications.

Secondly, other well established printing technologies have been radically refined to improve quality, cater for larger paper sizes and reduce costs dramatically. With printing resolutions of up to 600 dots per inch (dpi), quiet operation and the ability to produce high volumes of output without constant attention, the new generation of raster plotters addresses many of the needs of typical modem design offices.

Thirdly, the credibility of laser printers as CAD output devices was given a significant boost by Hewlett Packard, which included an HP-GL translator within recent generations of the LaserJet series of printers.

Although limited to small paper sizes, many CAD users have found the easy-to-use aspect of laser printers extremely attractive, particularly as the printers can now receive CAD data without any intermediate translation.

In the last three years, most common types of printing technology have been applied to CAD hard copy, with significant advantages over traditional plotters. Capable of high resolutions of 300 or 600 dpi on paper of all sizes from A3 to AO, printers (rather than plotters) are also well suited to high throughputs. More important is their ability to emulate both plotters and printers – text printing, CAD line-drawings and photo-realistic shaded renderings are all available from the same device. Prices are competitive, and although colour is still an expensive option, prices here will also drop before too long.

Pen plotters have remained competitive by reducing prices significantly over the last three years, so that a typical machine capable of accommodating paper sizes up to AO now costs under £4,000 – half the price of a few years ago. Manufacturers have also worked hard to improve performance.

The speed of pen plotters has improved, particularly as the newer units are able to optimise the order in which lines are drawn. One interesting new development has been Hewlett Packard’s HP-GL/2 plotter language. This is, put simply, a binary form of the original ASCII-format HP-GL, which allows drawings to be sent to plotters from the PC far more quickly than before.

The number of A3 laser printers is currently rising rapidly, and several offer plotter emulation as standard. Prices of these devices have also dropped, typically to under £3,000.

Electrostatic plotters work on very similar principles, but at large sizes. Prices have also dropped here, but not sufficiently to bring them within reach of PC-based systems. Thermal plotters have made some inroads into this market, although paper quality is still unacceptable for many users.

Ink-Jet is potentially the most interesting printing technology for CAD at present. Printer/plotters of this type are generally based on either the HP DeskJet or Canon Bubblejet engines, both of which are well-proven and reliable. Hewlett Packard themselves have designed new print-heads to cope with the heavier demands of plotting at the largest sizes. Machines are available for paper sizes from A3 to AO, in either monochrome or full-colour.

As with A4 Ink-Jets, special paper is not normally required, although plastic film for long-term storage needs careful selection. It’s worth remembering that as paper-size increases so does the time needed to print very large bit-mapped images. You can use additional memory in the printer as a buffer to reduce the amount of time the PC is required, but this can be expensive, reducing the price differential compared with a plotter.

The versatility and good value of pen plotters means that they are likely to remain popular for quite some time, especially for the largest paper sizes. Nevertheless, their prices need to drop further still if they are to compete successfully with A2 and A3 monochrome Ink-Jet machines. At paper sizes of A2 and A3, Ink-Jets are showing the way towards truly general purpose printer/plotters.

Some manufacturers have started to follow a trend first seen in PC display hardware, by including drivers and emulations for a wider range of software. In addition to standard printer emulations such as Epson, IBM Proprinter and Laserjet, drivers for HP-CL, Windows and AutoCAD are becoming more common – even PostScript is becoming popular in this market sector.

The new and diverse generation of hardware emulation and driver support on offer is making the boundary between printers and plotters less and less distinct, and improvements in plotter performance and speed have ensured they remain popular for some time.

Tim Baty