DXF Files Overview

DXF files are standard ASCII text files. They are easily translated to other CAD system formats or are submitted to other programs for processing directly. A Drawing Interchange File is simply an ASCII text file with a file extension of .DXF and specially formatted text. This is analogous to the ASCII .RTF (Rich Text Format) published by Microsoft for exchange of binary Word document (.DOC) files. The overall organization of a DXF file is as follows:

1. HEADER section—Contains general information about the drawing. It consists of the drawing's database version number and a number of system variables. Each parameter contains a variable name and associated value.
2. CLASSES section—Holds the information for application-defined classes, whose instances appear in the BLOCKS, ENTITIES, and OBJECTS sections of the database. A class definition is permanently fixed in the class hierarchy.
3. TABLES section—Contains definitions for the following symbol tables.
   • Linetype table (LTYPE)
   • Layer table (LAYER)
   • Text style table (STYLE)
   • View table (VIEW)
   • User Coordinate System table (UCS)
   • Viewport configuration table (VPORT)
   • Dimension Style table (DIMSTYLE)
   • Application Identification table (APPID)
   • Block Record table (BLOCK_RECORD)
   
   
4. BLOCKS section—Contains block definition and drawing entities that make up each block reference in the drawing.
5. ENTITIES section—Contains the graphical objects (entities) in the drawing, including block references (insert entities).
6. OBJECTS section—Contains the non-graphical objects in the drawing. All objects that are not entities or symbol table records or symbol tables are stored in this section. Examples of entries in the OBJECTS section are dictionaries that contain mline styles and groups.

A DXF file is composed of many groups, each of which occupies two lines in the DXF file. The first line is a group code. The second line is the group value, in a format that depends on the type of group specified by the group code.

For more information:

AutoCAD DXF Documentation
http://usa.autodesk.com/adsk/servlet/item?siteID=123112&id=8446698

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