Lisp routine to calculated weighted centroid of seperate lines

[Monty Lisp]

Hi All,

 

I'm trying to get the coordinates of a centroid of multiple seperate lines. It should be a centre of gravity of lines, but taking the length as weight. (So the sum of each line's midpoint x-coordinate times its length, divided by sum of all lengths, and the same for the y-coordinate).

 

Somehow I cannot find anywhere an example to do this yet I have the feeling it shouldn't be too difficult. I'm not too familiar with LISP but as autocad LT 2024 has the ability to load LISP files I suddenly see so many tiny processes which I can automate . 

 

I hope someone can help me, 

 

Kind regards,

Monty Lisp

[fuccaro]

Hello and welcome!

Try this:

(defun c:pp()
  (setq ssl (ssget '((0 . "LINE"))) xg 0 yg 0 zg 0 lt 0)
  (repeat (setq i (sslength ssl))
    (setq el (entget (ssname ssl (setq i (1- i))))
	  p1 (cdr (assoc 10 el)) p2 (cdr (assoc 11 el))
	  x1 (car p1) x2 (car p2) xm (/ (+ x1 x2) 2.0)
	  y1 (cadr p1) y2 (cadr p2) ym (/ (+ y1 y2) 2.0)
	  z1 (caddr p1) z2 (caddr p2) zm (/ (+ z1 z2) 2.0)
	  l (distance p1 p2)
	  xg (+ xg (* xm l)) yg (+ yg (* ym l)) zg (+ zg (+ zg l))
	  lt (+ lt l)
	  )
    )
    (setq ssl nil)
    (setq w (list (/ xg lt) (/ yg lt) (/ zg lt)))    
  )

For sure the masters around here will post shorter and more elegant code, I tried to write the program step by step. Post again if you need more clarifications...

[marko_ribar]

https://www.theswamp.org/index.php?topic=57619.msg610196#msg610196

 

HTH., M.R.

[Monty Lisp]

59 minutes ago, fuccaro said:

Hello and welcome!

Try this:

(defun c:pp()
  (setq ssl (ssget '((0 . "LINE"))) xg 0 yg 0 zg 0 lt 0)
  (repeat (setq i (sslength ssl))
    (setq el (entget (ssname ssl (setq i (1- i))))
	  p1 (cdr (assoc 10 el)) p2 (cdr (assoc 11 el))
	  x1 (car p1) x2 (car p2) xm (/ (+ x1 x2) 2.0)
	  y1 (cadr p1) y2 (cadr p2) ym (/ (+ x1 x2) 2.0)
	  z1 (caddr p1) z2 (caddr p2) zm (/ (+ z1 z2) 2.0)
	  l (distance p1 p2)
	  xg (+ xg (* xm l)) yg (+ yg (* ym l)) zg (+ zg (+ zg l))
	  lt (+ lt l)
	  )
    )
    (setq w (list (/ xg lt) (/ yg lt) (/ zg lt)))
    (setq ssl nil)
  )

For sure the masters around here will post shorter and more elegant code, I tried to write the program step by step. Post again if you need more clarifications...

 

Thanks! Such a quick answer. There was a tiny error for y1 (you use x1 and x2 again but with my limited knowledge of LSP I updated it to y1 and y2 and it worked!) 

 

I'll dissect the code and see if i can learn some LISP as this saves me quite some time! 

[BIGAL]

When you need say mid of 2 points this is handy as you dont need to work out X & Y values.

 

Both these do the same

(setq mp (mapcar '/ (mapcar '+ p1 p2) '(2.0 2.0 2.0))) ; divide by 2
(setq mp (mapcar '* (mapcar '+ p1 p2) '(0.5 0.5 0.5))) ; Multiply by 0.5