DXF

DXF (Drawing Interchange Format) is the format in which AutoCAD® saves and exports its drawings. AutoCAD® was initially an exclusively 2D drafting system. It was later extended to include 3D capabilities. However, its internal data structures and its output format retained, to a large extent, the characteristics of the original drafting oriented representations. The AutoCAD® entities which appear as 3D objects when displayed, are in fact groups of separate surfaces. Furthermore, they are surfaces of at most four sides and they cannot contain holes.

 

DXF files may also contain block definitions and insertions. The blocks (called symbols by other programs) represent the ability to define entities which can then be placed as copies or instances, called insertions. An insertion is not a complete representation of the entity, but rather points to the definition of that entity in some central library of representations, called block definitions. A DXF file may contain block definitions that have been placed (inserted) one or more times, as well as definitions that have not been placed. A placed block definition is called a referenced block. Otherwise, it is called a non-referenced block. form•Z only imports referenced blocks. Each block becomes a copy of that block transformed to the correct location, scale and orientation.

 

When exporting facetted data, faces that consist of at most four sides and contain no holes, can be exported directly as they are. However, faces with more than four points or faces with holes have to be decomposed to the type of surfaces that DXF can handle.

 

Importing DXF files

import_opts_DXF.tiff
The Modeling Import Options: DXF dialog.

A DXF file is imported into form•Z in the standard manner. In addition to the common options, the Modeling Import Options: DXF dialog contains a number of format specific options:

 

Form Object By Layer (Polylines, 3D Faces): When this option is on, simple objects are constructed from all the polylines and 3D faces on a layer. This option is not available when Make Reference Object is selected.

 

Import Hatch Patterns: When this option is selected, hatch entities are read as individual lines. This can result in a large number of line objects being generated. If this option is not selected, hatch patterns are not imported.

 

Make Smooth Objects: When this option is selected, objects which can be represented as smooth objects (e.g. splines, arcs, circles, etc.) will be imported as smooth objects. Selecting this option for a large file can greatly increase the import time. If this option is not selected, all entities except REGION, SOLID3D, and BODY will be imported as facetted.

 

Import All Objects As Lines: When 2D line data is imported from a DXF file, closed lines are imported as surfaces. This is often undesirable because the fill on the surfaces can obscure other line objects. When this option is selected, the Render As Wire frame attribute is set for all imported objects.

 

Exporting DXF files

export_opts_DXF.tiff
The Modeling Export Options: DXF dialog.

 

export_dxf_version_dialog.png
The Edge Visibility menu.

 

The content of a form•Z project is exported as a DXF file in the standard manner. In addition to the common export options, there are also a number of DXF specific options.

 

Export Facetted Objects As ACIS Objects: When this option is selected, facetted objects are written to the DXF file as embedded ACIS entities rather than native DXF entities. Note that not all software that can read DXF files supports the ability to read the embedded ACIS entities. This option is off by default.

 

Version: This pop up menu, allows you to indicate which version of AutoCAD the DXF file will be exported to. The default is 2007/2008.

 

Edge Visibility: This pull down menu contains three options that control the visibility of the edges of the exported 3D faces.

All Visible: Selecting this option causes all the edges, both the original edges and the edges resulting from the splitting, to be marked as visible.

 

All Invisible: Selecting this option causes all the edges, both the original edges and the edges resulting from the splitting, to be marked as invisible.

 

Actual Visible/Split Invisible: This is the default option and causes the split edges to be invisible, while the original edges of the faces remain visible.

Export Groups As Blocks: When this option is selected, form•Z groups will be exported as blocks. The groups are defined by the Grouping Method in the common options (e.g. if the Grouping Method is set to By Color, objects of the same color will be considered a group and will be exported as a block). To export groups, defined in the object palette as blocks, set the Grouping Method to By Group.

 

Include Lights: when this option is selected, the lights in the project will be included in the exported file.

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