DWF Background: AutoCAD Drawing Layouts (Part 1)

The early versions of AutoCAD worked with drawing (DWG) files that defined one space for modeling called "model space" and another for printing called "paper space." Model space was where designs were created. Paper space was like one "Print Preview." AutoCAD users had the need to print the model data in a variety of ways. In response to this, later versions of AutoCAD allowed DWG files to contain definitions for multiple paper spaces. These are referred to as layouts, since they reflect how the model data is laid out on physical paper.

Although DWF files were originally single sheet, later versions allowed for multiple sheets. As such DWF files today can contain data as it appears in model space, layouts, or both.

Autodesk DWF Viewer 6.5 supports the ability to view a composite DWF file which is a combination of 3D and 2D data; however, in terms of submissions for printing, it is typical for an AutoCAD user to create a multisheet DWF file that contains a collection of 2D sheets. These sheets are normally created from layouts instead of model space, so that these sheets can be considered print-ready. Typically 3D DWF files are distributed for interactive viewing instead of printing.

Each layout in a DWG file can be associated with a specific device to which the layout will be printed. This is done by associating the layout with a plotter configuration (PC3) file that is configured for the device. Some hardware manufacturers develop specific AutoCAD drivers for a given device. These device drivers are referred to as HDI drivers, since they use the Heidi Device Interface. Heidi is the graphics system used for display and hardcopy in many Autodesk products. Alternatively some manufacturers use a generic Windows System Printer driver to accept data from AutoCAD.

The decision to use an HDI driver or Windows System Printer driver can have an effect on printed output. As such, it can also have an effect on the content of a DWF file. For example, the line merge capability is implemented in some HDI drivers but not some Windows System Printer drivers.

1. Tips for creating layouts:
   1. You create geometry in the model environment at full scale.
   2. You set paper size for the layout and a plot scale of 1:1 for the paper.
   3. You view model geometry on the layout through viewports.
   4. The scale factor of the model geometry on the layout is based on the scale factor that you set for the viewport.
   5. You can create multiple viewports to display different sections of the model geometry or show it at different scales.
   6. On a layout with multiple viewports, you can freeze layers in each viewport independently to create different displays of the same model space area.
   7. You should only add text to the geometry in the model space environment if it is a major aspect of the design. Otherwise you should place general annotation on the layout at full scale.
   8. Insert the border and title block on the layout at full scale. The border and title block are typical created one is a template file and XREF’d into various drawings.
2. You can configure a layout for a specific device, e.g. Océ TDS800, or for the generic DWF6 ePlot pc3 driver.
3. When a DWF file is created, the page size and other information are captured from each layout and transferred to a "virtual piece of paper" inside the DWF file. The virtual piece of paper is displayed as backdrop when viewing a DWF file.
4. When the PRINT command is issued from the Autodesk DWF Viewer or Autodesk Design Review, the settings from the virtual piece of paper are used to map the DWF file to the physical paper. This same information is also used by DWF partner applications such as Océ Repro Desk and PLP PlotWorks.
5. If there is a possibility that DWF files will be printed at both full and half sizes, you should allow twice the normal margin when setting up your title block/border templates. This is because the physical margins on the printer remain the same for full and half size.
6. A viewport scale is not to be confused with a plot scale. The normal workflow for setting up a layout is:
   1. AutoCAD is unitless. When you draw a line that goes from (0,0) to (1,0) AutoCAD knows the line is 1 "unit" long; however, is that 1 unit one meter? One foot? One light-year? This is up to the user’s interpretation. Note that there is a display style that can look like feet and inches (1’ 2"), but that is just a display style of the underlying otherwise unitless values.
   2. When drawing in Model space, the user has some personal concept of what the unitless units represent (for example, 1 unit = 1 foot). When drawing in Model space there is no scale: everything should be drawn in actual units. A line that represents 10 feet in the real world should be 10 units long (assuming a unit represents one foot).
   3. You then create a layout which represents a piece of paper.
   4. You then add a viewport into the layout which is a "window" into Model space.
   5. If you select the viewport object and go to the property pane, you’ll see there is a "standard scale" setting and a "custom scale" setting. This scale changes the "zoom" level of the viewport. In other words, it locks the scale between the Model space coordinates and their size when drawn on the virtual paper of the layout. By setting the viewport scale to ¼" = 1’ means that .25 inches on the layout’s virtual paper is 1 Model space unit (a foot in this example).
   6. Once you set the viewport scale, growing or shrinking the size of the viewport in the layout does not change the scale of the graphics. It will either expose more of model space or clip more of model space.
   7. If you activate the viewport (by double clicking in it), you can use the pan and zoom tool. When in viewport active mode, this changes the view of model space inside the viewport. Doing a zoom changes the viewport scale which is often not desired. If the user sets a viewport scale they can also "lock" the scale to prevent users from accidentally zooming in viewport active mode.
   8. When you aren’t in viewport active mode, then pan/zoom just changes your view of the virtual page and doesn’t change the scale of anything.

Layouts are key in that DWF files created from them are print-ready. This is a relative term. A sheet in a DWF is certainly more print-ready than model space in a DWG. DWF files are less print ready than a device-specific format like HPGL. A little more processing time is required. But DWF lets you get the right printout and provide other benefits that go beyond the paper.