06 December 2007
AutoCAD Polyline Types          
Confused about the various polyline types that you see in AutoCAD?

From the end user perspective there are 3 polyline types listed in the PROPERTIES command, even though there are only two "entity" types.

  • polyline - this is an LWPOLYLINE entity, always 2D.
  • 2d polyline - this is a POLYLINE entity, also 2D.
  • 3d polyline - this is a POLYLINE entity, usually 3D, with each vertex at a different elevation. It is possible to have a "3d polyline" and have each vertex at the same elevation.

If you use the LIST command on any polyline, you will only see the
entity names (POLYLINE or LWPOLYLINE).

POLYLINE entities are the original type. LWPOLYLINE entities were introduced in R14.

If PLINETYPE = 0 (zero), then the PLINE command will create POLYLINE entities.
If PLINETYPE = 1 or 2, then the PLINE command will create LWPOLYLINE entities.

To create 3d polylines, use the 3DPOLY command.

To convert between POLYLINE and LWPOLYLINE entities, use the CONVERTPOLY command.

If you are using Autolisp, you only need to worry about the entity names (POLYLINE and LWPOLYLINE.) A "3d polyline" is simply a POLYLINE entity with a special flag set. When this flag is set, each vertex subentity can be set to a different elevation.

Depending on what else you may be doing, you may also see
names like:
Acad3DPolyline, or AcDb3dPolyline
AcadPolyline, or AcDb2dPolyline
AcadLWPolyline, or AcDbPolyline

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PermaLink       Posted 12/06/2007 05:23:00 PM     

Comment from: Blogger Rockmaster
Date: December 13, 2007 at 6:56:00 PM CST  

Good article. I'd like to add one thing:

If you want to convert a 3D polyline to an LW polyline, you can't use CONVERTPOLY. You have to first run the FLATTEN command, then EXPLODE the flattened polyline, then use PEDIT Multiple to join all of the line segments into an LW polyline.

Comment from: Anonymous junes
Date: January 2, 2008 at 8:31:00 AM CST  

So is there any difference between 2dpolyline and lwpolyline...?

Comment from: Anonymous Anonymous
Date: February 16, 2008 at 2:41:00 PM CST  

The main difference is that lwpolylines have all there verts inside their entity data (10 and 40 codes). Old style polylines don't contain the vert data, but are followed by a collection of vertex sub-entities. This makes them take up more space internally, and makes them harder to work with.

So what do you do when convertpoly refuses to convert your pline?

Comment from: Anonymous belajar autocad
Date: September 11, 2008 at 8:07:00 AM CDT  

i like autocad. how to build autocad 3d??

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