Topic: How to cut an 3D solid with a profile line?

[CADwoman]

Hello all, does anyone know if there is a LISP tool out there that can help me cut a 3D solid with a 2D profile line? I've been playing around with Microstation and one of the really nice 3D operations was to be able to cut a 3D solid using a line. Another words you pick the solid then define a 2D line or closed polyline and then it would project the profile though the 3D solid. Any help would be appreciated.

[Rob_Kish]

Either SLICE or SECTION AutoCad commands will do the job. If you have only a line (e.g. two points) you must create a third ... like offset one of the endpoints in the plane normal (Z, presumably) direction.

[David Hall]

I use slice, when it tells me to pick 3 points, pick your 2 endpoints of the line , and type @0,0,1 for third point.  The 3rd point is based on the 1st point to set up the vertical plane.

[Tramber]

if you want to perform an operation with a closed polylign, then use such a macro :

Code: [Select]

^C^C_select \_extrude p;;1e8 0 (sorry, I don't know if it's correct for US measurment. itdoesn't(modified) creates an object below Z=0

then it is easy to _SUBTRACT or _INTERSECT with L like last object created or to grow the button code if you wish, I can help.

[CADwoman]

The only option that actually did what I want was slicing with a 2 point 2d polyline. If you use a circle, arc, ellipse or 2D spline, it would just slice it along its co-plane as opposed to its projection. Does that make sense?

[Tramber]

Well, slicing is easy with all the options. Moving or rotating the UCS allows to obtain fast results, especially with the XY,YZ or XZ options because 1 point is enough.

Are you on a version below 2007 ?

[CADwoman]

Yes, I am using 2007.

Well, slicing is easy with all the options. Moving or rotating the UCS allows to obtain fast results, especially with the XY,YZ or XZ options because 1 point is enough.

Are you on a version below 2007 ?

[qjchen]

This is my program to cut a cone to get the parabolic line. I am not sure whether it is useful for you.

Code: [Select]


(defun c:test ()
  (vl-load-com)
  (setq *acad-object* nil)
  (setq *active-document* nil)
  (setq *model-space* nil)
  (setq ratio (getreal "\n y=kx^2 k=?:"))
  (setq vl-p1 (vlax-3d-point '(0 0 0)))
  (setq vl-p2 (vlax-3d-point '(1000 0 0)))
  (setq vl-p3 (vlax-3d-point '(1000 1000 0)))
  (setq vl-p4 (vlax-3d-point '(0 0 -500)))
  (setq vl-p5 (vlax-3d-point (list 0 0 (/ 0.5 ratio))))
  (setq mycone (vla-addcone (model-space) vl-p1 1000 1000))
  (vla-move mycone vl-p1 vl-p4)
  (vla-rotate3d mycone vl-p1 vl-p2 (/ pi 4))
  (vla-move mycone vl-p1 vl-p5)
  (setq cur (vla-sectionsolid mycone vl-p1 vl-p2 vl-p3))
  (vla-erase mycone)
  (vla-explode cur)
  (setq a (ssget "X" '((-4 . "<OR") (0 . "region")
          (0 . "line")
          (-4 . "OR>")
         )
      )
  )
  (command "erase" a "")
)

(defun acad-object ()
  (cond
    (*acad-object*)
    (t
      (setq *acad-object* (vlax-get-acad-object))
    )
  )
)


(defun active-document ()
  (cond
    (*active-document*)
    (t
      (setq *active-document* (vla-get-activedocument (acad-object)))
    )
  )
)


(defun model-space ()
  (cond
    (*model-space*)
    (t
      (setq *model-space* (vla-get-modelspace (active-document)))
    )
  )
)


[MickD]

As bert' mentioned, to cut a solid with the profile of a polyline you first need to create a solid from the 'closed' polyline, ie. extrude it deep enough to pass through your object to be cut. Then you simply SUBTRACT the new solid from the cutting object.
When doing this, make sure your cutting polyline is in the correct plane and you may need to give it a negative height value, you will see this after extrusion anyway and with a bit of practice you'll get the hang of it and from here you could contruct your lisp routine to perform the cuts automagically.
Rob's idea for cutting with a line is the best way to go, grab one of your lines points and change its 'z' value to give you another point to create a plane from the line to cut your object. The user will soon work out that a correct ucs is required when using this routine to achieve the correct result.
hth,
Mick.