DXF

DXF is a file format to exchange CAD data from Autodesk. It is the "open" equivalent of DWG files.

DXF file data

A DXF file is subdivided in several sections. The most important sections are:

HEADER
TABLES, containing definitions of layers
ENTITIES: containing 2 and 3 dimensional shapes
BLOCKS: containing 2 and 3 dimension shapes, reusable using INSERTS in ENTITIES.

Entities

Currently, the following Autodesk CAD entity types are supported:

LWPOLYLINES (2 dimensional line strings), including bulges. See also AutoCAD Documentation.
LINE (single lines). See also AutoCAD Documentation.
POLYLINE (3 dimensional line strings), currently only interpreted as 2 dimensional. The z-coordinate is ignored. See also AutoCAD Documentation.
HATCH (polygonal data constructed using other boundary entities). See also AutoCAD Documentation.
CIRCLE: full and partial circles, given a center point, radius and start and end angle. See also AutoCAD Documentation.
ELLIPSE: full and partial ellipses, given a center point, major and minor axis, rotation and start and end angle. See also AutoCAD Documentation.
ARC: curved lines given a center point and a radius. See also AutoCAD Documentation.
VERTEX: 2 dimensional point. See also AutoCAD Documentation.
POINT: Same as vertex, but 3 dimensional. Currently only interpreted as 2 dimensional. The z-coordinate is ignored. See also AutoCAD Documentation.
SPLINE: 2 dimensional Control point splines are currently supported. See also AutoCAD Documentation.
INSERT: Predefined BLOCKS inserted at a point and with a rotation and a scale. See also AutoCAD Documentation.

Blocks

BLOCKS are parts in a CAD drawing that can be reused multiple times by inserting them at different locations with optional alternative rotations and scales. The usage of BLOCKS in a DXF is supported. See also AutoCad Documentation.

Layers

In the DXF file, entities are always assigned to one particular layer. In AutoCAD, layers can be turned on and off. This visibility does not influence whether or not the entities in this layer can be imported.