FILE STRUCTURE OF DXF

ASCII versions of DXF can be read with a text-editor. The basic organization of a DXF file is as follows.

1. HEADER section – This section contains the general information about the drawing. Each parameter has a variable name and an associated value.
2. CLASSES section – This section holds the information for application-defined classes whose instances appear in the BLOCKS, ENTITIES and OBJECTS sections of the database. Generally does not provide sufficient information to allow interoperability with other programs.
3. TABLES section – This section contains definitions of named items.
   1. Application ID (APPID) table
   2. Block Record (BLOCK_RECORD) table
   3. Dimension Style (DIMSTYPE) table
   4. Layer (LAYER) table
   5. Linetype (LTYPE) table
   6. Text style (STYLE) table
   7. User Coordinate System (UCS) table
   8. View (VIEW) table
   9. Viewport configuration (VPORT) table
4. BLOCKS section – This section contains Block Definition entities describing the entities comprising each block in the drawing.
5. ENTITIES section – This section contains the drawing entities including any block references.
6. OBJECTS section – This section contains the data that apply to non-graphical objects, used by AutoLISP and ObjectARX applications.
7. THUMBNAILIMAGE section – This section contains the preview image for the DXF file.
8. END OF FILE.

The data format of a DXF is called a “tagged data” format which means that each data element in the file is preceded by an integer number that is called a group code. A group code’s value indicates what type of data element follows. This value also indicates the meaning of a data element for a given object (or record) type. Virtually all user-specified information in a drawing file can be represented in DXF format.