Anuncios

The Autodesk Community Forums has a new look. Read more about what's changed on the Community Announcements board.

Diameter of isocircle

Anonymous

Diameter of isocircle

Anonymous
No aplicable

How do I find the diameter of the isocircle?

 

Is this the good way? (The diameter is 20) Please tell me if there are any other ways to do this

 

legit.png

0 Me gusta
Responder
3.169 Vistas
8 Respuestas
Respuestas (8)

Kent1Cooper
Consultant
Consultant

@Anonymous wrote:

How do I find the diameter of the isocircle?

 

....

Here's one way, in simplest terms [none of the usual controls yet, etc.]:

 

(defun C:ICD (/ el) ; = IsoCircle Diameter

  (setq el (car (entsel "\nSelect Ellipse to find its axonometric Diameter: ")))

  (* 2 ; to get diameter from:

    (distance ; isometric-axis radius

      (cdr (assoc 10 (entget el))); center

      (vlax-curve-getPointAtParam el (* pi 0.25)); quarter-of-pi Parameter value at axis point

    ); distance

  ); *

); defun

 

Or, the diameter directly:

 

(defun C:ICD (/ el) ; = IsoCircle Diameter
  (setq el (car (entsel "\nSelect Ellipse to find its axonometric Diameter: ")))
  (distance ; isometric-axis diameter
    (vlax-curve-getPointAtParam el (* pi 0.25)); axis point as above
    (vlax-curve-getPointAtParam el (* pi 1.25)); opposite axis point
  ); distance
); defun

 

I think that would be correct for an Ellipse of any axonometric axis ratio, not just an isometric one, hence the wording of the prompt not using the words "isometric" or "isocircle."

Kent Cooper, AIA

Kent1Cooper
Consultant
Consultant

@Kent1Cooper wrote:
.... 

I think that would be correct for an Ellipse of any axonometric axis ratio, not just an isometric one, hence the wording of the prompt not using the words "isometric" or "isocircle."


... which means I should have used a different command name.... [too late to Edit that Post]

Kent Cooper, AIA
0 Me gusta

GrantsPirate
Mentor
Mentor

The isocircle diameter will be the longest distance between quadrants.


GrantsPirate
Piping and Mech. Designer
EXPERT ELITE MEMBER
Always save a copy of the drawing before trying anything suggested here.
----------------------------------------------------------------------------
If something I wrote can be interpreted two ways, and one of the ways makes you sad or angry, I meant the other one.

0 Me gusta

Kent1Cooper
Consultant
Consultant

@GrantsPirate wrote:

The isocircle diameter will be the longest distance between quadrants.


Actually, no, it won't.  See the original image, in which they drew a vertical [pinkish] axis Line [or Xline], and Circles [also pinkish] going through the points where that vertical axis intersects the Ellipses, and they're showing the diameter of that Circle [for only the inner one], which is the "real-world" diameter of the inner isocircle.  That is the circle of which the Ellipse is an isometric projection, and as can be clearly seen in the image, the corresponding Ellipse is longer along its major axis and shorter along its minor axis than the diameter of that circle.  Only a distance parallel to one of the isometric axes [such as the distance across that Ellipse along that vertical axis] is a "real" length in the "world" that the drawing represents in isometric projection.  The Ellipse's major and minor axes are not parallel to its isometric axes, and therefore the distances between quadrant points are distorted by the projection, and don't represent "real-world" lengths on the represented circle.  [The same is true for axonometric projections at other than isometric viewing angles, with isometric just being a special case of axonometric projection.]  That's what the "-metric" in axonometric and isometric means -- you can measure such a drawing only parallel to the axonometric/isometric axes, if you want to get "real-world" dimensions.

 

Fortunately, parameter values in (vlax-curve) terms going around an Ellipse correspond to radians going around the virtual circle of which the Ellipse is a projection, which is why my routine above is fairly simple -- it's looking at multiples of 45 degrees [1/4 of pi radians] around the represented circle to find the axonometric axis enpoint locations, between opposite ones of which the diameter can be measured.

Kent Cooper, AIA
0 Me gusta

GrantsPirate
Mentor
Mentor

A true isometric projection will result in the object being drawn about 2/3 the actual size.  Even with an isometric drawing the ellipse can't be larger than the circle is it made to represent.  I think of a can of beans and looking at the top it is a circle.  Then I can rotate the can so the top shows as an ellipse but it can never be larger that the diameter of the circle.  


GrantsPirate
Piping and Mech. Designer
EXPERT ELITE MEMBER
Always save a copy of the drawing before trying anything suggested here.
----------------------------------------------------------------------------
If something I wrote can be interpreted two ways, and one of the ways makes you sad or angry, I meant the other one.

0 Me gusta

Kent1Cooper
Consultant
Consultant

@GrantsPirate wrote:

A true isometric projection will result in the object being drawn about 2/3 the actual size.  Even with an isometric drawing the ellipse can't be larger than the circle is it made to represent.  I think of a can of beans and looking at the top it is a circle.  Then I can rotate the can so the top shows as an ellipse but it can never be larger that the diameter of the circle.


That may be the case if you tilt the world about only one axis [you're picturing the X or Y axis, I imagine].  But not when it's tilted isometrically, which involves all three axes, and that matters.  Think of a square drawn in isometric projection, like the one in the OP's original image around the larger Ellipse, and in this image:

 

IsoDistortion.png

 

You can dimension that square along its edges, and they'll represent the "real-world" size of the square, because they're parallel to the isometric axes.  But the diagonal from upper left to lower right is longer than the diagonal of such a square when viewed head-on, and the other diagonal shorter, and you can't dimension along those and get "real" results, because they're not parallel to the isometric axes.  Same for the major and minor axes of an Ellipse, compared to the circle of which it is a projection -- they get stretched exactly as the diagonals in that square do, one stretched longer and the other shorter than the "reality" they represent.

 

Putting in the Ellipse representing a circle in isometric projection, and the corresponding Circle viewed head-on:

IsoDistortion2.png

Kent Cooper, AIA
0 Me gusta

GrantsPirate
Mentor
Mentor

You are using the term 'Isometric Projection' when you mean 'Isometric Drawing'.  Two very different things with different results.  Iso Projection actually takes into account the tilting of the various axis when it is projected (hence the reduction in size of about 2/3 when projected) where an Iso Drawing is 'faked' by drawing real lengths along the isometric axis.

 

 


GrantsPirate
Piping and Mech. Designer
EXPERT ELITE MEMBER
Always save a copy of the drawing before trying anything suggested here.
----------------------------------------------------------------------------
If something I wrote can be interpreted two ways, and one of the ways makes you sad or angry, I meant the other one.

0 Me gusta

Kent1Cooper
Consultant
Consultant

@GrantsPirate wrote:

You are using the term 'Isometric Projection' when you mean 'Isometric Drawing'.  Two very different things with different results.  Iso Projection actually takes into account the tilting of the various axis when it is projected (hence the reduction in size of about 2/3 when projected) where an Iso Drawing is 'faked' by drawing real lengths along the isometric axis.


Not according to this.  See the "Some 3D shapes..." image on the right, where on the cube, the black dimensions along the axis directions of the object represented are equal to the red dimensions of the 2D projection drawing of it, the same as in my images.  In any case, despite any question of terminology, what the OP is doing is clearly what you are calling an 'Isometric Drawing,' in which case what I said holds true.

Kent Cooper, AIA
0 Me gusta