AutoCAD DXF - File Structure

File Structure

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

• HEADER section – General information about the drawing. Each parameter has a variable name and an associated value.
• CLASSES 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.
• TABLES section – This section contains definitions of named items.

Application ID (APPID) table

Block Record (BLOCK_RECORD) table

Dimension Style (DIMSTYPE) table

Layer (LAYER) table

Linetype (LTYPE) table

Text style (STYLE) table

User Coordinate System (UCS) table

View (VIEW) table

Viewport configuration (VPORT) table

• BLOCKS section – This section contains Block Definition entities describing the entities comprising each Block in the drawing.
• ENTITIES section – This section contains the drawing entities, including any Block References.
• OBJECTS section – Contains the data that apply to nongraphical objects, used by AutoLISP and ObjectARX applications.
• THUMBNAILIMAGE section – Contains the preview image for the DXF file.
• 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."