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February 28, 2007

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Robin Capper

Why the 2 x larger file size for DWFx?

Scott Sheppard

DWFx file sizes will vary based on the content. When DWF was first invented, it was a binary format to keep the file sizes down. This was 1995 so bandwidth was not what it is today. As such, the DWF team wanted to do everything to make the file as small as possible. For example, the opcode for a line is not "LINE" but "L" which allowed the opcode to save 3 bytes. I admit that 3 bytes does not seem like a lot, but if you have thousands of lines in your design data, it starts to add up. The DWF team knew small differences like this would add up based on the nature of CAD data - quite intense in its graphics. If you recall your history, early AutoCAD had its own Autodesk Device Interface (ADI) because the Windows system printer drivers could not handle the printing demands of CAD users. AutoCAD had to invent its own. Such was the case with DWF. Using industry standards like VRML, a proposed ASCII-based 3D standard, resulted in design data files that were too large for the times. So unlike any generic document format, DWF was crafted specifically to the needs of CAD data.

Today we are in a different world. Bandwidth is much greater than it was in 1995. Customers are more concerned with interoperability. XML is all the rage. So whereas the binary number 75 (for "L") is the one byte opcode for a line in DWF, in DWFx opcodes look something like this:

Path Name="N6621E1D4671645788327E45A88D0BE90_4" Stroke="#00FF00" StrokeEndLineCap="Round" StrokeStartLineCap="Round" StrokeLineJoin="Round" StrokeThickness="12"...

No longer do applications have to know that 75 represents a line. Applications can simply parse the XML associated with the Path opcode and gain information about the design data.

DWF files optionally embed fonts. For example, AutoCAD users can embed all, some, or none of the fonts. With DWFx, the only choice is "all." This will be welcome news to people who have shared DWF files with others who did not have the same set of fonts on their systems; however, it does make the DWFx files larger.

So the short answer to your question is that the original DWF was specifically honed to be as optimal as possible in terms of file size. The Microsoft XPS standard is designed is based on XML, which by its nature, results in larger file sizes. The forecast is not all gloom and doom though. DWFx files (with the .dwfx extension) tend to be 30% - 100% larger than their corresponding DWF files (.dwf extension). Comparing raw XPS files (with the .xps extension) to DWF is not a valid comparison, since the Microsoft XPS Writer produces XPS files using a different process. A similar condition exists for DWF today. The DWF Writer is implemented as a virtual printer. Hence DWF files published by the DWF Writer go through the Microsoft Graphics device Interface (GDI). Using GDI makes the DWF files larger than DWF files produced by the DWF6 ePlot pc3 driver used directly by AutoCAD. So in the same way that the DWF Writer is not recommended for people using AutoCAD, the AutoCAD DWFx Driver will be recommended instead of the Microsoft XPS Writer.

Please keep in mind that both the DWF and the DWFx are smaller than the DWG.

AutoCAD has come a long way. It is common for people to use Windows printer drivers to plot CAD data. It no longer has its own ADI printing system. Windows has made advancements in its printer drivers. Working together, Autodesk and Microsoft are going to apply similar advancements with design data. This is just the start.

Thanks for your question Robin.

Ralph Grabowski

I recall that that the first DWF format was in ASCII and binary; later, it became available in compressed formats.

The reason L was used for the Line opcode was because the first DWF format only drew lines. So, using L definately saved space!

Grant Buote

What's the difference between the "DWF6 ePlot" driver and the "DWF6 ePlot DETE" drivers that are standard installs in 2008? I can't seem to find a reference to it anywhere.

Thanks

Volker Joseph

I believe that the "DWF6 ePlot DETE" is a Map Guide specific *.pc3 file. There are other "DWF6 ePlot + XXX" *.pc3 drivers out there, mostly for vertical products deriving of the AutoCAD platform.

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