DXF File Format

DXF file icon

Design reads and writes the DXF (Drawing Exchange Format), an open file format originally developed by Autodesk as the interoperability standard for CAD drawings. DXF files can be opened by virtually all CAD applications and are the primary way to share drawings created in Design.

Overview

DXF is a plain-text (ASCII) format. Each file is a sequence of group code / value pairs — an integer group code on one line followed by its value on the next. The group code identifies what the value means:

0        ← group code: entity type
LINE     ← value: this is a LINE entity
10       ← group code: X coordinate of start point
100.0    ← value
20       ← group code: Y coordinate of start point
50.0     ← value

Group codes are consistent across entity types — for example, group code 10 always represents the primary X coordinate of an entity regardless of which entity type it belongs to.

File Structure

A DXF file is divided into named sections, each beginning with a SECTION marker and ending with ENDSEC. The sections appear in the following order:

Section

Purpose

HEADER

Drawing-wide variables: units, limits, current layer, snap settings, etc.

CLASSES

Application-defined object classes (rarely edited manually).

TABLES

Named object definitions: layers, line types, text styles, dimension styles, and block record table.

BLOCKS

Block definitions, including the implicit *Model_Space block that holds all entities on the canvas.

ENTITIES

All drawing entities in model space (legacy; modern files store entities in BLOCKS).

OBJECTS

Non-graphical objects such as dictionaries and extended data.

Common Group Codes

The following group codes appear in almost every entity:

Code

Meaning

0

Entity type name (e.g. LINE, CIRCLE, ARC)

5

Entity handle — a unique hex identifier

6

Line type name (BYLAYER if inherited from the layer)

8

Layer name

10, 20

Primary point X and Y coordinates (start point, centre, or insertion point)

11, 21

Secondary point X and Y coordinates (end point or direction)

39

Thickness (extrusion depth; 0 for flat 2D entities)

62

Colour number (256 = BYLAYER)

370

Line weight (-1 = BYLAYER)

DXF Entities

Each drawing entity has its own set of required group codes in addition to the common ones above. The pages below describe how each Design entity is represented in DXF:

  • commands/line — LINE entity

  • commands/circle — CIRCLE entity

  • commands/arc — ARC entity

  • commands/polyline — LWPOLYLINE entity

  • commands/rectangle — LWPOLYLINE entity (closed flag set)

  • commands/text — TEXT entity

  • commands/hatch — HATCH entity

  • commands/dimension — DIMENSION entity

  • commands/block — BLOCK definition + INSERT entity

Further Reading