for 2d polylines convertpoly is usable but how can I convert 3d polylines?p.s. flatten -> unknown command thanks

[QUOTE=hotcoffee]for 2d polylines convertpoly is usable but how can I convert 3d polylines?p.s. flatten -> unknown command thanks
[/QUOTE]Have you see this routine in this page:http://newsline.cadalyst.com/code/browseyear.cfm?fullyear=2003#9

Best/easiest way would be a lisp routine as in the link Arben posted.
 
Flatten would not help you much anyway; it would change all z values to 0 but would still be a 3d polyline, not responsive to CONVERTPOLY.
 
However you could explode the flattened 3dpoly, use pedit or mpedit to join back to a lwpolyline.
 
You should be able to install Express Tools off the original installation disk, so you would have the Flatten command.

There are 4 methods described in the related tip 5673 - see:
http://www.cadforum.cz/cadforum_en/qaID.asp?tip=5673