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File Formats for Sharing CAD Drawings

DWF, HPGL, WMF, or PDF?

Geoff Harrod

Members of Queensland CAD Users Group (Australia) have been exploring ways of sending AutoCAD work to clients and others - allowing the recipients to view and print the drawings without requiring AutoCAD or the ability to use it and such that the drawing data cannot be altered. The following reports on investigations and recommendation.

For many people and businesses in design and engineering disciplines, drawings are the final deliverables. Traditionally drawings (or prints) were simply transmitted to the client and the job was done. Today, the need to share drawings quickly and cheaply demands an electronic format that is easy to access and as effective as a traditional paper drawing. Several data formats are readily accessible that offer solutions that might prove suitable to use for this purpose. The format/technologies considered in this article are DWF, HPGL, WMF and PDF.

DWF

The most obvious in the current context of AutoCAD R14 and 2000 is to generate DWF files, which were designed by Autodesk mainly for use on the Internet. You can create a DWF file from a drawing by the File>Export menu in R14 or the plotting system in 2000.

A Windows program called VoloView Express is included with AutoCAD R14 and 2000, which you are permitted to copy and give away to anyone. It enables viewing of DWG, DXF and DWF files, and printing them, to some degree. However it does not provide a good enough solution since its control of printing options such as zooming and line-widths is inadequate.

Autodesk's fully featured solution is named VoloView (without the Express), available as a stand-alone program for several hundred dollars. To have the level of access that VoloView provides requires each client or associate to buy a copy. This may quite likely provide all that is needed but none of us have seen the program, and for this purpose it may be too expensive for all clients to agree to buy.

Autodesk's now discontinued View program can also view and print DWF files, but we found it had some significant defects in its control over the display of blocks in viewports. Autodesk View can also view and print WMF files, mentioned later, but it exhibits serious flaws in displaying WMF files that have infills.

There are other graphics and view/print programs, such as Cimmetry Systems' AutoVue, which handles a wider range of formats very well, including several CAD formats, However, for this purpose we agreed that these viewing programs would be too expensive for some clients to accept.

It is a reasonable assumption that DWF files would be viewed with a web browser in conjunction with the free Autodesk Whip! browser plug-in, but that is still disadvantaged with inadequate printing controls.

HPGL

Another possibility is to generate HPGL plot files. This again requires the recipient to install a program for viewing and printing, but there are some free ones, such as SPLOT and PrintGL, both which are available on CADinfo.Net.

HPGL is of course intended as a data stream to drive a pen plotter or an inkjet plotter. Hence an HPGL plot file represents whatever you may have defined as the data to plot, whether by Window, Extents or from a PaperSpace sheet. It is limited to the precision of a plotter, and the scale of a plot sheet, and the file can be rather big, especially if the older, text-format, HPGL format is used. The newer HPGL/2 format is binary and more compact, and can also store actual line-widths rather then pen-numbers, and raster elements. Hence HPGL/2 is preferred.

But although it provides satisfactorily for printing (but with zoom and page size preset by the sender), HPGL is very poor for interactive viewing. The limited precision of the HPGL plotter format becomes all too apparent if you try to zoom in closely to view.

WMF

WMF is Microsoft's 'Windows MetaFile' graphics format. A MetaFile is a format that supports a mixture of vector line data, polygon infills and raster image fragments. Hence it is quite suitable for representing CAD data, including 3D rendered views. It is basically the same in capability as the older (and more reliable) CGM format, which is compatible with Windows, Macintosh and Unix. Surprisingly, Microsoft do not supply any WMF-capable viewing or editing program with Windows, except that Word can use WMF graphics, but not large ones. The usual tools for WMF are artistic drawing programs such as Adobe Illustrator, Corel Draw and Macromedia Freehand, all costly and not CAD oriented.

One area where WMF is often used with AutoCAD data is for placing drawings in Desktop Publishers or Word. However the facility incorporated in AutoCAD for creating WMF files is too poor to be of much use. A company called Furix identified the need for quality WMF output from AutoCAD and ships a program called "BetterWMF for AutoCAD". This is a commercial product and is good value considering the quality of its output and all its facilities. It can be obtained from CADstore.Net as a time-limited evaluation version, and then converted to full-time use by paying and downloading a key-code. That site also illustrates its capabilities.

WMF ought to be suitable for the purpose under discussion, but isn't, because of the poor output facilities in AutoCAD, and the need for a costly viewing and printing program by the recipient.

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Geoff Harrod acknowledges the input of Alan Harbour, Viv Duncan, Stephen Gye, and John Tacey, members if the Queensland CAD Users Group, in researching and reporting the information published here.

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