The Drawing Exchange Format (DXF) from AutoDesk is a verbose ASCII geometry format capable of representing lines, simply defined surfaces, and polygons (3D faces).

The file structure of a DXF file is divided into 4 main sections:

• HEADER: identifying the system variables
• TABLES: providing general information such as line style, user-defined coordinate systems, and so on.
• BLOCKS: defining instanced blocks in the model
• ENTITIES: describing the entities of the model
  Note

  The above applies to the DXF format from Autocad 14

Each section is preceded by a group code 0, followed by the SECTION string, a group code 2 and the type of section. A section is concluded with the 0 groupcode and the ENDSEC string. In each section, there are different items, each consisting of 2 lines: the first to declare the nature of the item, the second to define it's value. Each item in a DXF file takes a new line, therefore even the description of a simple vertex takes up to 12 lines.

The group codes (GC) defines the nature of the value on the next line. There are general and section specific group codes.