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DCarpenter

How to draw a true ellipse

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I know this has been talked about to GREAT lengths, but whats the solution?  Has someone written a PIO that draws a true ellipse?  ...

 

I'm designing a fairly large production that revolves around a large elliptical stage with a lot of other custom elliptical pieces and would like them to be true.  Looking for some direction from those who live in the forum.  I've wasted a bunch of time reading past post that don't seem to come to a resolution.  Any final words on this issue?

 

Thanks for the help,

Dave

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I think I've read that an oval in VWX is an ellipse. Different drawing modes give different results.

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I read a thread that said mathematically the VW oval isn't an ellipse, but what drawing modes are you referring to?

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I saw something from VWX that said it is, but it's a good question. The tool has three modes in the tool bar; box, height and width and Center Mode. I would venture that Center mode would be the most precise.

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Somewhere on the forums there is a "proof" of sorts that shows that within the margin of error from the calculations, a Vectorworks oval is an ellipse. There are issues if you offset an oval, since an offset oval is not an ellipse but Vectorworks draws it as one.

 

Kevin

 

 

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yes, I was going to suggest NOT offsetting the original. If there are many parts of the project based on the one bit of gpeetry, I would have a layer with different sizes, all drawn, to use as needed.

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So we think the current rule of thumb is the trust the VW oval, but to NOT use the offset command.

Kind of surprised VW hasn't addressed this issue.  This topic seems to have a long and rich history in these forums.

 

I'll give it a try...

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Posted (edited)

True. The oval of VW is an ellipse. An ellipse can be made by taking a circle and scaling it in one direction. (to check individual points on that ellipse you can convert the circle to a Polygon and check if the points lie on the ellipse (oval). They do.)

Back in the MiniCad days the offset of the oval was a polygon (good) and later a polyline (nicer but less precise). But at some moment in time VW decided to let the offset of an ellipse be an ellipse again and this is not true. This is easily check by drawing dimensions between the first oval and its offset.

Edited by Gerard Jonker
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