Surface from 3 points

[BB8x]

Hello

Maybe someone has or can write something for me. I need to draw surface from 3 points (triangle, planar).

I can imagine this like that:

1) I do click 3 points in the drawing

2) Lisp creates 3d poly or 3d face (what is easier)

3) Lisp turns 3d poly or 3d face into surface

4) Lisp deletes base 3d poly or 3d face

Thanks

[doaiena · Accepted solution]

Here you go.

(defun c:test ( / p1 p2 p3 lastEnt)

(setq p1 (getpoint "\nPick first point: "))
(setq p2 (getpoint "\nPick second point: "))
(setq p3 (getpoint "\nPick third point: "))

(if (and p1 p2 p3)
(progn

(if (vl-cmdf "3dface" p1 p2 p3 "" "")
(progn
(setq lastEnt (entlast))
(vl-cmdf "convtosurface" lastEnt "")
(vl-cmdf "erase" lastEnt "")
))
))
(princ)
);defun

[Sea-Haven]

A surface is a more plural answer of multiple 3dfaces, so why convert ? Are you trying to make a multi 3dface surface if so just google for Triangulation it will make a surface form points.

[BB8x]

Thanks doaiena lips works great

Usually I do triangulation, but sometimes is easier to draw than delete unwanted elements from triangulation

[_gile · Accepted solution]

Hi,

It would be much cheaper to simply do some geometric computation.

You can easily calculate the signed area of a triangle (it's equal to the half of the Z coordinate of the cross product of (p1,p2) and (p1,p3) vectors). The sign of the result also indicate if points are clockwise or not.

(defun signedArea (p1 p2 p3)
  (/ (-	(* (- (car p2) (car p1)) (- (cadr p3) (cadr p1)))
	(* (- (car p3) (car p1)) (- (cadr p2) (cadr p1)))
     )
     2.0
  )
)

(defun c:test (/ p1 p2 p3)
  (and
    (setq p1 (getpoint "\nPick first point: "))
    (setq p2 (getpoint "\nPick second point: "))
    (setq p3 (getpoint "\nPick third point: "))
    (alert
      (strcat
	"Area = "
	(rtos (abs (signedArea p1 p2 p3)))
	"\nPoints are "
	(if (minusp (signedArea p1 p2 p3))
	  "clockwise"
	  "counterclockwise"
	)
      )
    )
  )
  (princ)
)

[john.uhden]

BTW, if you're looking to shave off a few nanoseconds, I think I found years ago that multiplying by 0.5 is faster than dividing by 2.

[braudpat]

Hello @john.uhden 

Your answer is THE BEST !

THE HEALTH (Stay Safe), Regards, Patrice

[john.uhden]

Yes, well, after enough millenia, those nanoseconds can add up, maybe to as
much as a full blink of an eye. *;)*

[diagodose2009 · Accepted solution]

Can you extend this routine?

;; Revision :07/03/2020 @Anonymous:44
(defun c:fc1 ( / p1 p2 p3)
(progn  
       (setq p1 (getpoint "\nPick first point: "))
       (setq p2 (getpoint "\nPick second point: "))
       (setq p3 (getpoint "\nPick third point: "))
       (setq p4 (getvar "VIEWCTR"))
       (if (and p1 p2 p3)
       (progn  (setq CmColor 1)
               (entmakex (list (cons 0 "3DFACE") 
                         (cons 100 "AcDbEntity") 
                                    (cons 67  0) 
                                    (cons 8 "0") 
                               (cons 62 CmColor) 
                           (cons 100 "AcDbFace") 
                             (cons 10  p1) 
                             (cons 11  p2) 
                             (cons 12  p3)
                             (cons 13  p3) 
                                   (cons 70 0)))
               (princ)
               (entmakex (list (cons 0 "3DFACE") 
                         (cons 100 "AcDbEntity") 
                                    (cons 67  0) 
                                    (cons 8 "0") 
                               (cons 62 50) 
                           (cons 100 "AcDbFace")
                             (cons 10  p1) 
                             (cons 11  p2) 
                             (cons 12  p3)
                             (cons 13  p4) 
                                   (cons 70 0)))
               (princ)
       ))
      )
) ; end eMaker

[_gile]

---

@diagodose2009  a écrit :

Can you extend this routine?

---

Sorry, I do not understand what you mean.

[Sea-Haven]

You mean repeat

(while (setq p1 (getpoint "\nPick first point: "))

extra close bracket at end

               (princ)
       ))
      ))
) 

[BB8x]

Hello again

Is there a chance to upgrade this lisp? For now creates surfaces. Would be possible to create surfaces OR mesh OR 3d solid (selectable)?

Lets say like this:

1) Lisp start

2) "What would you like to do you lazy ****? Surface Mesh 3dSolid"

3) Carry on with lisp

4) Chosen output

[Sea-Haven]

Just go back to what I said get a triangulation routine pick all points, this makes 3dfaces. Google for next steps. They exist.

[BB8x]

I know google knows that and been trying for few days. Thing is I did find only way to extrude or thicken surface. I wanted to keep in as it is (planar). All I am doing now is extruding for 0.0001 drawing units