Expertise

Export to DWG

Revit Workflow

Export to DWG

Objectives

  1. Understand the customized settings before exporting to DWG.
  2. Be able to create a useful “Export Setup”

Prerequisites

  1. User has basic skills in BIM modelling with Revit Software, and understands the language used.
  2. User has basic skills in Autocad formats.

Configuration

DWG export consists in making a translation of Revit sheets/views to CAD formats, which are radically different.

When working with BIM models, the ideal situation is that there is no need to export to DWG, and all stakeholders are able to consume the BIM model.

But this is just an ideal world. Actually, it is required in many cases to export to CAD formats.

At this point, export to DWG is done from the Menu>Export>CAD Formats>DWG.

From this window, two actions are performed:

1. Select views/sheets to export.

2. Select export configuration that will be used.

1 Export settings menu

1.1 Select elements to be exported

You can export to DWG both views and sheets.

Views properties

  • The views are exported to space model.
  • 3D axonometric views are exported to a 3D DWG in the space model.

Sheets properties

  • They are exported to paper space. The content of the graphic windows are exported to model space.

Select views/sheets to export

From the drop-down Export menu we have two options:

  • Current view/sheet only
  • This option  only export the view that is active at that moment.
  • In session view/sheet set
  • With this option you can choose between views and existing sheets.

In any case the selection of views and sheets can be recorded to be used later.

1.2 Export setup

Export settings Button is located at the top left (it is also reachable directly from the Export>Options> Export Setups DWG/DXF).

  • From the drop-down menu you can select a specific configuration.

Different export configurations are listed because previously they were directly saved in the file or can transferred from other project files through the option “Transfer project standards”.

  • It is recommended to record the performed settings. The configuration is saved as an internal project standard of Revit.

  • In the export settings window, we can find the following tabs:
  • Layers
  • Lines
  • Patterns
  • Text Fonts
  • Colors
  • Solids
  • Units Coordinates
  • General

2 Export settings

2.1 General

  • Export of Rooms, Spaces and Area Boundaries as closed polylines. It is recommended not to select it unless they are specifically useful in the DWG file.
  • Area polylines are generated from area plan views only.
  • Room polylines are generated from floor plan views or ceiling plan views only.
  • For Revit MEP, this option also applies to spaces.
  • For rooms, the exported polylines match the boundaries of rooms in Revit. The room boundaries are exported onto a single layer, and that layer is turned off by default in the DWG file. The polylines include the following XDATA information for room boundaries:
  • Name
  • Number
  • Occupancy
  • Occupant
  • Department
  • Comments.
  • For areas, the polylines include the following information for area boundaries:
  • Name
  • Comments.

  • Configure non-printing layers. This is a very useful option when you want to export certain elements but by automatically sending them to layers that are defined in AutoCAD as non-printing. Select the Make layers containing the following text not plottable option to mark as non-plottable any layers whose names contain the specified text.

  • Options: Click any of them to refine the export customization:
  • Hide Scope boxes: Select this option to hide scope boxes in the exported file.
  • Hide Reference plans: Select this option to hide reference planes in the exported file.
  • Unreferenced view tags. E.i. if you have a section but it is not placed in any sheet, its symbol will not be exported.

  • Preserve coincident lines: Select this option to include coincident lines in the exported file.

Usually, elements share a plane, resulting in model lines that coincide in the drawing. In this case,a desk share lines with some walls.

When you export the model to DWG, by default the coincident lines are not preserved.

That is, if you display only the wall layer, the export data does not include the lines that are coincident with the other elements.

 

  • Set the export views and links as xref. Clear this check box if you want any Revit or DWG links in the project to be exported to a single file rather than to several files that reference each other.

  • Set the version of the DWG file. Choose the correct Autocad version that is compatible with the installed software in order to be able to open the exported drawings

2.2 Units and coordinates

  • The resulting DWG file units: Choose the units of the exported file. Keep in mind that when we export a sheet, units will be the same for model space and paper space.
  • For imperial projects, the default unit is inches. For metric projects, the default unit is meters.
  • The system of coordinates:
  • A internal project. The internal origin point is used as origin point in Autocad when exporting with Internal Coordinates option.
  • Coordinates shared. The survey point is used as origin point in Autocad when exporting with the Shared Coordinates option.

2.3 Solids

  • Polymesh: Exports all visible Revit  geometry as polymeshes. A polymesh is a 3D shape consisting of multiple polygons that are meshed (joined) together. This geometry is referred to as face-based.
  • ACIS solids: ACIS is a solid modeling technology. Any elements that are already polymeshes (such as toposurfaces and import symbols that contain polymeshes) remain as polymeshes.

2.4 Colors

  • Index color (255 Colors). For colors that are set by category, the indexed colors specified on the Layers tab of the Modify DWG Export Setup dialog will be used.

When colors are not set by category (if elements in views are overriden by any mean -filters, by element, etc.-) and the override is preserved in the export, Revit uses the closest match from the 255 indexed colors and thus may not provide an exact match for RGB and Pantone colors.

                

  • True color (RGB Values). Uses the RGB value from Revit, rather than the indexed color from the Layers tab of the Modify DWG Export Setup dialog.

Sometimes it may be practical to use this option, since the appearance in terms of colours and line weights that takes the DWG (with regard to printing) is the same as in Revit, without the need for a CTB file that makes the colors transformation.

If you are exporting a view that contains a linked project, the link is treated as an override. To ensure that colors and other graphic display settings are preserved in the exported file, on the Modify DWG Export Setup dialog (Layers tab), select "Export all properties BYLAYER, but do not export overrides."

2.5 Text & Fonts

  • Exact (Formatting intelligence will be lost). Exported text will look exactly as it does in Revit (exact line wrapping). However, if the text includes bulleted or numbered lists, that paragraph functionality is lost upon export. Pressing Enter within a formatted paragraph will not restore the formatting.
  • Approximate (Formatting intelligence will be maintained). If exported text includes bulleted or numbered lists, that paragraph functionality is maintained when the text is edited. Pressing Enter within a formatted paragraph will restore the formatting. However, the visual appearance of the text may vary from the original, whether or not the note contains a list (that is, wrapping may vary)
  • Mapping Revit Text Fonts. By default, all the Revit fonts listed in the mapping table have a value of “Automatically map font”  in the Text Fonts in DWG column, which means the Revit font will be maintained in the exported file. If you want to map a Revit font to a specific DWG text font, click the value for that font in the Text Fonts in DWG column, and then select the desired font from the drop-down list.

It is recommended to apply this option unless it is necessary to use specific Fonts in DWG different to those used in the model to be exported.

2.6 Patterns

There is a relationship between the "Patterns" used in Revit and the "Patterns" used in DWG applied when exporting.

  • By default, if the selected option is "Automatically generate hatch pattern". The "patterns" of Revit will export exactly and so Autocad will automatically create a new "pattern".
  • However Revit also gives the option to select a "pattern" of existing Autocad to a "pattern" of Revit. So previously you must select from the top menu the .pat file to be used.

In both cases you can select Pattern Type as:

  • Drafting. The scale remains fixed, regardless of the view scale.
  • Model. The scale of the hatch is fixed regarding the model. It change according to the view scale.

2.7 Lines

The procedure in Lines is the same as patterns. In this case the extension it is required is a .lin to map the line types.

At the top of the window, you can also select "Linetype Scale" to control the scale to which line types are exported. The options are:

  • Scaled Linetype definitions. This option preserves graphical intent by exporting linetypes the same as they were previously scaled by view scale.
  • Modelspace (PSLTSCALE = 0). This option sets the LTSCALE parameter to view scale and the PSLTSCALE to 0.
  • Paperspace (PSLTSCALE = 1). This option sets the value of both LTSCALE and PSLTSCALE to 1. Revit LT linetype definitions are scaled to reflect project units, but otherwise they are exported as is.

2.8 Layers

It configures the export from Revit objects (classified by categories and subcategories) to layers of Autocad.

The schedule shows on the one hand the list of all categories of Revit and other DWG layer in which graphical representation of these categories is to be placed.

Distinction is made between layers for graphic representation in projection and section.

There is a column not only for the layers name but for the color too "Color ID column”.

  • In the first drop-down menu you can choose between these options:
  • Export category properties BYLAYER and overrides BYENTITY. A Revit element with view-specific graphic overrides will retain those overrides in the CAD application, but will reside on the same CAD layer as other entities in the same Revit category.
  • Export all properties BYLAYER, but do not export overrides. View-specific graphic overrides will be ignored in the CAD application. Any exported Revit element will reside on the same CAD layer as other entities in the same Revit category. By forcing all entities to display the visual properties defined by their layer, this option results in a lower number of layers and provides by-layer control over the exported DWG file.
  • Export all properties BYLAYER, and create new layers for overrides. A Revit element with view-specific graphics will be placed on its own CAD layer. This option provides by-layer control over the exported DWG file, and preserves graphical intent. However, it increases the number of layers in the exported DWG file.
  • In the second drop-down menu above the box you can select a defined configuration of layers according to different standards.

3 Best Practices

3.1 Limit Geometry

  • In Revit, a view of the building model contains many objects and a lot of data. When exporting a model for use in another software application, Revit exports only the objects that are visible in the views. By reducing the amount of model geometry (and its underlying data) that is exported, you can achieve the following:
  • Improve performance of the export process.
  • Reduce the size of the exported file.
  • Improve performance of the importing application.
  • Reduce clutter (non-essential items) in the exported file, and hence the amount of work required to delete these objects from the file in the importing application.
  • Techniques to reduce the amount of geometry to be exported.
  • Turn off visibility of graphics that you don’t need for your specific purpose.

If you hide elements temporarily, revit will ask you if you want preserve this situation while exporting.

  • Use a section box or a crop region to define a specific region.
  • Specify the detail level
  • Remember that Revit export exactly what you see.

3.2 Adjust scale

  • Adjust the view scale to control the precision/performance ratio. When you export to 2D DWG, you export a scaled 2D view of the model. The view scale you apply determines whether the resulting view is exported for precision or for performance. For example, if your model contains 2 lines that are 1mm apart and the view scale is 100, the lines will be considered to be within tolerance, and the exported DWG will contain a single line (exported for performance). If the view scale is 20, the exported DWG will contain separate lines (exported for precision).

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Tips&Tricks

  • If a hatch pattern is not visible in the exported DWG file, and the message "Hatch Pattern Too Dense" displays in the AutoCAD text window, try adjusting the AutoCAD system variable HPMAXLINES to increase the maximum number of hatch lines that are generated in a hatch operation.
  • If a hatch pattern is not exported to a DWG file check if the pattern (or material) has transparency applied.
  • Revit always tries to map the Revit dimension parameters to the proper DWG Dimension styles properties. But in some cases there may be parameters that cannot be mapped. At that point Revit will export the dimension to preserve its visual fidelity. The visual fidelity will only be a temporary display, as soon as the dimension is regenerated it will read its properties from the dimension style and the display may change.

Case

Display in Revit

Display in AutoCad

Dimension Extension

The display of a dimension extension is changed for a radial and an arc length dimension.

  • When you export a 3D view to a DWG file, colors are treated as follows:
  • Edge colors: because they are not rendered in AutoCAD, edge colors are ignored on export. This will result in correct shaded/realistic views (edge overrides will no longer be assigned to the entire model).
  • Phase colors: color overrides on solid fills are supported on export, but color overrides on patterns are not.
  • If you use one of the export tools for a 3D view, Revit exports the actual 3D model, not a 2D representation of the model. To export a 2D representation of the 3D model, add the 3D view to a sheet and export the sheet view. You can then open a 2D version of the view in AutoCAD. It will be a vector drawing, not an image.
  • Remember that if you:
  • Export views you can export either in internal coordinates or in shared coordinates.
  • Export sheets you will only be able to export with the “Internal” coordinates option.
  • Remember that the layer mapping settings that are configured in an english version of the software will not work with other language versions of the software, and vice versa.

Bottom-line

  • Customize the export settings in accordance with your company standards is a task that should be done at least once. It takes time, but it can be used later on including it on the template or through “Transfer Project Standards”
  • Create or modify layer mapping to ensure that all the information stored in Revit categories and subcategories will be exported to the proper CAD layers (or levels, if exporting to DGN).

Associated Files

  • Coordinates guideline

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