2d versus 3d arcs

[Bill Toler]

How do I tell the difference between 2d and 3d arcs in autocad lisp?  If I ask for the normal vector for a 2d arc it crashes the program, but you can have a 3d arc at z=0, so just checking the z value doesn't do it.

[BIGAL]

Maybe look at the 210 dxf code (210 0.0 0.0 1.0) this is world ucs, an arc drawn in a UCS will be like, (210 0.0 -0.334116324669344 0.94253184645902)

[Bill Toler]

      (setq normal (cdr (assoc 210 ent))) ; Extract the normal vector - problem here
      ; : this command throws an error and crashes the program on a 2D arc
 

[Steven P]

That works for me with 2d arc:

 

(setq MyEnt (car (entsel "Select Arc")))
(setq normal (cdr (assoc 210 (entget MyEnt))))

 

What error message are you getting?

[Bill Toler]

ERROR: bad argument type

[Bill Toler]

Hey Steve P: Thanks!  I figured out the problem was I had "normal" as a parameter in the function parameter list - apparently can't use it twice.  That was the reason for the error.  Now I'm on my way on this again.

[Emmanuel Delay]

What's a 3D arc?

Isn't an arc by definition a 2D thing?

[pkenewell]

@Emmanuel Delay I think what the OP means by a "3D" arc is an arc that is not in the WCS, or not in the primary UCS plane relative to the view.

[Emmanuel Delay]

1 minute ago, pkenewell said:

@Emmanuel Delay I think what the OP means by a "3D" arc is an arc that is not in the WCS, or not in the primary UCS plane relative to the view.

 

I that cas I either:

- set the UCS to whatever the arc requires.

- make the arc in WCS, align the arc to its final position

[pkenewell]

4 minutes ago, Emmanuel Delay said:

I that cas I either:

- set the UCS to whatever the arc requires.

- make the arc in WCS, align the arc to its final position

@Emmanuel Delay Sure, but the OP was only asking how to detect whether the Arc is normal to the WCS or not.