Mobius Strip?

[dangermouse]

Hi everyboby,
This is purely a sitting infront of autocad with nothing better to do question,is it possible to draw a "MOBIUS STRIP" with autocad.
it would be cool to do, have fun trying its baffled me, but then again thats not hard .


always smiling dangermouse

[fuccaro]

;        MOEBIUS SURFACE   
;      mfuccaro@hotmail.com
;;;;;;;;;;;;- 21.05.2003 -;
(defun c:mb()
  (setq xmax 200 ymax 11;you may change here the dimensions
    x 0 rad2 (/ xmax (* 2 PI))
    save (list (getvar "osmode") (getvar "cmdecho")))
  (setvar "cmdecho" 0)
  (setvar "osmode" 0)
  (command "3dmesh" (1+ xmax) ymax)
  (repeat (1+ xmax)
    (setq y (- (/ ymax 2)))
    (repeat ymax
      (setq ang1 (/ (* x PI) xmax)     ;twist along OY
        x1 x
        y1 (* y (cos ang1))
        z1 (* y (sin ang1)))
      (setq ang2 (/ (* x1 2 PI) xmax)  ;bend on OZ
        x2 (* rad2 (sin ang2))
        y2 y1
        z2 (* (+ rad2 z1) (cos ang2)))
      (command (list x2 y2 z2))
      (setq y (1+ y)))
    (setq x (1+ x)))
  (command "vpoint" (list 1 1 1))
  (setvar "osmode" (car save))
  (setvar "cmdecho" (cadr save))
  (princ)
  )

You may change the xmax and ymax -with Notepad or with any other text editor- but keep the ymax impair.

*** editing ***
As I mentioned before (read bellow) the code must be cleaned before you can use it. Here it goes:

;        MOBIUS SURFACE   
;      mfuccaro@hotmail.com
;;;;;;;;;;;;- 21.05.2003 -;
(defun c:mb()
  (setq xmax 200 ymax 11;you may change here the dimensions
    x 0 rad2 (/ xmax (* 2 PI))
    save (list (getvar "osmode") (getvar "cmdecho")))
  (setvar "cmdecho" 0)
  (setvar "osmode" 0)
  (command "3dmesh" (1+ xmax) ymax)
  (repeat (1+ xmax)
    (setq y (- (/ ymax 2)))
    (repeat ymax
      (setq ang1 (/ (* x PI) xmax)     ;twist along OY
        x1 x
        y1 (* y (cos ang1))
        z1 (* y (sin ang1)))
      (setq ang2 (/ (* x1 2 PI) xmax)  ;bend on OZ
        x2 (* rad2 (sin ang2))
        y2 y1
        z2 (* (+ rad2 z1) (cos ang2)))
      (command (list x2 y2 z2))
      (setq y (1+ y)))
    (setq x (1+ x)))
  (command "vpoint" (list 1 1 1))
  (setvar "osmode" (car save))
  (setvar "cmdecho" (cadr save))
  (princ)
  )

[dangermouse]

Hi,
absolutly superb, thank you very much indeed.

always smiling dangermouse

[fuccaro]

And here is an image:

[CADTutor]

Fantastic! Is there no end to this mans talent?

[fuccaro]

Thank you CADTutor! As always I feel good reading your appreciation. What did you find “fantastic” -the lisp or the image?
The routine is not hard to understand -just a bit of math, especially trigonometry. About 30% of the program lines are for save and restore settings, comments and so. The point is: even a very short program can do the task, for the AutoCAD/AutoLisp it is almost a trivial one.
About the image: The file-size is a bit over the 50k limit you set but as I know I am the first one who published animated images in the Forum. I will not abuse by this in the future. I created some screen-captures viewing the surface from different angles, I edited the images and I have put them together.

[CADTutor]

What is most fantastic is the through response to the request. I must admit that my first reaction was, "Mobius Strip in AutoCAD? Don't even go there!" Once again, your rather more pragmatic approach wins the day.

[dangermouse]

Hi,

The mobius strip question was more of a challenge for the "BRAINS" and for mear mortals like me to gaze in wonder at the results.I must find out where they hand out thease brain things.joking aside i think the way you take a problem and find a solution is great.are there seperate courses for learning lisp routines or is it just a case of knowing computer programming.

always smiling dangermouse.

watch this space for the next challenge.

[Mr T]

Looks like a strip for about 2/3s then a twisted RULESURF ?????

Nick

[fuccaro]

Nick
The dimensions are not important. If the Mobius strip is not a commonly used concept: it looks like a ribbon twisted first around its longitudinal axis and than the ends are joined together.
Show us your way to draw the Mobius strip. It will be not the first when you make just with AutoCAD things I created with Lisp.