Topic: Center point "moved"

[Fuccaro]

I draw a circle with the center point at (10.5).
The elist is something like:

Code: [Select]

((-1 . <Entity name: 7efe7e40>) (0 . "CIRCLE”)… (10 10.0 5.0 0.0) (40 . 5.3) (210 0.0 0.0 1.0))
So far is fain.
If I rotate the circle about its Y axis with 180%%d I see the circle in exactly the same position as before.  But the elist tells me that the centerpoint is moved!

Code: [Select]

((-1 . <Entity name: 7efe7e40>) (0 . "CIRCLE")…(10 -10.0 5.0 1.22461e-015) (40 . 5.3) (210
1.22461e-016 0.0 -1.0))
Is it correct? How can I obtain the real position of the center?
Please help!
Thank you.

[Kerry]

not possible ...

Your rotation point was not the circle center.

[Fuccaro]

Try it yourself. I did it 3 times before I posted the question in the forum.
Thank you for answering me.

[CAB]

How did you rotate the circle, by what method?

[CADaver]

Notice he said "about the Y axis".  I used two different methods to rotate the circle, one was 3drotate, the other was reset the UCS to a "front" view, then rotate the circle, same results using osnap to the center of the circle each time.

I get before rotation about Y:

Code: [Select]

(
(-1 . <Entity name: 4007cd70>)
(0 . "CIRCLE")
(330 . <Entity name: 4007ccf8>)
(5 . "2E")
(100 . "AcDbEntity")
(67 . 0)
(410 . "Model")
(8 . "0")
(100 . "AcDbCircle")
(10 10.0 5.0 0.0)
(40 . 5.3)
(210 0.0 0.0 1.0)
)
After rotation about Y:

Code: [Select]

(
(-1 . <Entity name: 4007cd70>)
(0 . "CIRCLE")
(330 . <Entity name: 4007ccf8>)
(5 . "2E")
(100 . "AcDbEntity")
(67 . 0)
(410 . "Model")
(8 . "0")
(100 . "AcDbCircle")
(10 -10.0 5.0 -3.44505e-015)
(40 . 5.3)
(210 -1.22461e-016 -4.44089e-016 -1.0)
)


[Fuccaro]

Sorry for beeing not clear. I rotated the circle using the ROTATE3D command, around the Y axis passing trought the center of the circle.

[gile]

Hi,

All this seems correct.

DXF 10 code for a circle is defined according to its OCS (you can have a look about OCS here).

See the 210 DXF code of the rotated circle : (210 -1.22461e-016 -4.44089e-016 -1.0) instead of (210 0.0 0.0 1.0)

you can try these code lines on both rotated an non-rotated circle, the result should be the same :

(setq ent (car (entsel)) elst (entget ent))

Then

(trans (cdr (assoc 10 elst)) (cdr (assoc 210 elst)) 0)
or
(trans (cdr (assoc 10 elst)) ent 0)

[CADaver]

Hi Gile,
  My question is
(210 -1.22461e-016 -4.44089e-016 -1.0) instead of (210 0.0 0.0 1.0). 
and (10 -10.0 5.0 -3.44505e-015) instead of (10 10.0 5.0 0.0)

If I haven't moved the circle off its center point and I've rotated the UCS about the 0 Y axis, why should these points be different prior to (trans ?

[gile]

My question is
(210 -1.22461e-016 -4.44089e-016 -1.0) instead of (210 0.0 0.0 1.0).
and (10 -10.0 5.0 -3.44505e-015) instead of (10 10.0 5.0 0.0)

I don't know exactly why, but I saw it often with 3d rotations or 3D rotated UCS.

I suppose, as AutoCAD calculates in radians, it uses an approximation of pi (there can be only approximations of pi).
AutoCAD seems to have a precision of 16 decimal.

(rtos pi 1 16) returns "3.141592653589793" (rtos pi 2 17) returns the same.
If in WCS 0 is an effecive 0, rotating UCS of n*pi radians should make loose some précision and 0 become 3.44505e-015.

Knowing that I useally use a "fuzz" with points comparations :
(equal pt1 pt2 1e-9)
Note 1e-9 is equivalent to a micron for a kilometre.

[Fuccaro]

Thanks for all the answers!
I am wondering why this doesn't work:

Code: [Select]

(setq el (entget (car (entsel))))  ;select the circle
(setq el (subst '(210 0 0 1) (assoc 210 el) el))
(entmod el)I will read the pages about the TRANS function -it seems to be what I need. Thanks again.

[gile]

I am wondering why this doesn't work:
Code:
(setq el (entget (car (entsel))))  ;select the circle
(setq el (subst '(210 0 0 1) (assoc 210 el) el))
(entmod el)

This does work.
It changes the circle normal from (-1.22461e-016 -4.44089e-016 -1.0) -which is very very closed to (0 0 -1)- to (0 0 1).
But the center point -10 DXF code- (-10.0 5.0 -3.44505e-015) isn't changed.

You can try this :
- In the WCS, draw a circle center on (10 5) radius 5.3
- Select the circle and put the cursor on the circle center grip
- On command prompt, you read 10.0,5.0,0.0
- Now, rotate the UCS 180° on Y axis (this UCS is similar to the 3d rotated circle OCS)
- Select the circle and put the cursor on the circle center grip
- On command prompt, you read -10.0,5.0,0.0 which is very very closed to -10.0,5.0,-3.44505e-015
- In this UCS, if you draw a circle which center is 10,5 it will have the same position as the one got with :
(setq el (subst '(210 0 0 1) (assoc 210 el) el))
(entmod el)

I hope this example illustrates better thee question than I can do in my poor English

[ElpanovEvgeniy]

1 http://www.theswamp.org/index.php?topic=14649.msg177029#msg177029
2 (c:flatten)
3 (vla-put-Normal (vlax-ename->vla-object(car(entsel)))(vlax-3d-point 0. 0. 1.))

[CAB]

Knowing that I useally use a "fuzz" with points comparations :
(equal pt1 pt2 1e-9)
Note 1e-9 is equivalent to a micron for a kilometre.

As an alternative you can use (< (distance pt1 pt2) 1e-9)

[ElpanovEvgeniy]

Excuse, I badly tested...

Code: [Select]

(defun ent-exact (/ e)
  ;; By ElpanovEvgeniy
  ;; (ent-exact)
  (if (setq e (car (entsel)))
    (progn
      (entmod
(mapcar
  (function
    (lambda (x)
      (if (or (<= 10 (car x) 59)
      (<= 110 (car x) 149)
      (<= 210 (car x) 239)
      (<= 460 (car x) 469)
      (<= 1010 (car x) 1059)
  )
(if (atom (cdr x))
  (cons (car x) (atof (rtos (cdr x) 2 8)))
  (cons (car x) (mapcar(function(lambda(x) (atof(rtos x 2 8)))) (cdr x)))
)
x
      )
    )
  )
  (entget e)
)
      )
      (entupd e)
    )
  )
  (princ)
)
add:
This program will work with any entities...

[gile]

If you are disturbed by this kind of real numbers -3.44505e-015 or lists (-1.22461e-016 -4.44089e-016 -1.0), you can use the little following routine to "round" them to a true zero. It works as well with real numbers, lists or nested lists of numbers.

(truezero -3.44505e-015) returns 0.0
(truezero '(-1.22461e-016 -4.44089e-016 -1.0)) returns (0.0 0.0 -1.0)

Code: [Select]

(defun truezero (l)
  (if (listp l)
    (mapcar 'truezero l)
    (if (< -1e-12 l 1e-12)
      0.0
      l
    )
  )
)