Offsetting Ellipses

[tonypasqualino]

Hello,

When I offset an ellipse Autocad creates a spline.  Is there a way to create an ellipse instead?

Thank you,

Tony

[Alfred.NESWADBA]

Hi,

no, because offseting with a constant distance would not result in an ellipse, mathematical not possible.

Or with other words: to get an ellipse as result object the offset-distance can't be constant, you can try that by creating an ellipse with 100 length/20 height and another one with 140 length and 60 height ... what might be an offset of 20 ... now measure some distances around those tho objects.

- alfred -

[JDMather]

Autodesk Inventor will offset as an equal distance spline or as a true ellipse.

[Kent1Cooper]

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@tonypasqualino wrote:

....

When I offset an ellipse Autocad creates a spline.  Is there a way to create an ellipse instead?

....

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The routine here was made specifically to do just that.  It will do either full Ellipses or partial [elliptical arcs].  It even has the Through option for the offset distance [now, that was really something to figure out how to do!].  The distance between quadrant points will be what's equal [the specified distance if done that way, or in the Through option, the curve will go through the picked point (within a small tolerance) and the distances between quadrant points may be different from that but will be equal to each other], while of course the distance between the original and offset ones will vary elsewhere [which is the reason why AutoCAD's Offset produces a Spline instead, which can be equally (again, within a small tolerance) distant from the original Ellipse all around].

[Alfred.NESWADBA]

Hi JDMather,

>> Autodesk Inventor will offset as an equal distance spline or as a true ellipse.

The result is a true ellipse and the distance at every point between the inner and outer object is a constant?

As I don't have Inventor can you export the above sample please? I can't imagine that the offseted ellipse follows the mathematical rules for an ellipse object and want then to play around with that object and it's curving.

Thx in advance, - alfred -

[JDMather]

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@Alfred.NESWADBA wrote:

Hi JDMather,

>> Autodesk Inventor will offset as an equal distance spline or as a true ellipse.

The result is a true ellipse and the distance at every point between the inner and outer object is a constant?

Thx in advance, - alfred -

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The keyword is OR, not AND.  You can have one OR the other.

http://home.pct.edu/~jmather/AU2006/MA13-3%20Mather.pdf

See Tip #34, pg 14.

[JDMather]

This is how Autodesk Inventor completes Offset of an ellipse.

Notice in the first offset that a temporary vertical axis appears - this is indication that a true ellipse will be created.

In the second offset I picked further away from the vertical axis and Inventor returns a equal distance spline offset.

[Alfred.NESWADBA]

Hi,

>> The keyword is OR, not AND.  You can have one OR the other.

Thank you and please appologize about my minimalistic English and that I didn't see that difference clear enough.

- alfred -

[JDMather]

I was impressed that you realized that there is a difference.

Most who offset an ellipse do not realize what they are really doing.

[1Fabricator]

       If a spline is not acceptable; draw another ellipse.