The following group codes apply to vertex entities.
Vertex group codes 


Group code 
Description 
100 
Subclass marker (AcDbVertex) 
100 
Subclass marker (AcDb2dVertex or AcDb3dPolylineVertex) 
10 
Location point (in OCS when 2D, and WCS when 3D) DXF: X value; APP: 3D point 
20, 30 
DXF: Y and Z values of location point (in OCS when 2D, and WCS when 3D) 
40 
Starting width (optional; default is 0) 
41 
Ending width (optional; default is 0) 
42 
Bulge (optional; default is 0). The bulge is the tangent of one fourth the included angle for an arc segment, made negative if the arc goes clockwise from the start point to the endpoint. A bulge of 0 indicates a straight segment, and a bulge of 1 is a semicircle 
70 
Vertex flags: 1 = Extra vertex created by curvefitting 2 = Curvefit tangent defined for this vertex. A curvefit tangent direction of 0 may be omitted from DXF output but is significant if this bit is set 4 = Not used 8 = Spline vertex created by splinefitting 16 = Spline frame control point 32 = 3D polyline vertex 64 = 3D polygon mesh 128 = Polyface mesh vertex 
50 
Curve fit tangent direction 
71 
Polyface mesh vertex index (optional; present only if nonzero) 
72 
Polyface mesh vertex index (optional; present only if nonzero) 
73 
Polyface mesh vertex index (optional; present only if nonzero) 
74 
Polyface mesh vertex index (optional; present only if nonzero) 
91 
Vertex identifier 
Every vertex that is part of a polyface mesh has its vertex flag 128 bit set. If the entity supplies the coordinate of a vertex of the mesh, its 64 bit is set as well, and the 10, 20, 30 groups give the vertex coordinate. The vertex index values are determined by the order in which the vertex entities appear within the polyline, with the first being numbered 1.
If the vertex defines a face of the mesh, its vertex flags group has the 128 bit set but not the 64 bit. In this case, the 10, 20, 30 (location) groups of the face entity are irrelevant and are always written as 0 in a DXF file. The vertex indexes that define the mesh are given by 71, 72, 73, and 74 group codes, the values of which specify one of the previously defined vertexes by index. If the index is negative, the edge that begins with that vertex is invisible. The first 0 vertex marks the end of the vertices of the face.