Problems Exporting Ellipse from Rhino to AutoCAD

I’m having trouble exporting ellipses from Rhino to AutoCAD - can anybody send me some settings for the options dialogue that will work please?

I am working in mm, but sometimes work in metres as well, so if the settings are different (I think they would be) could you send some settings for metres as well?

I have attached four files - the original ellipse comes from CAD and is in mm (it is used around a number to indicate ceiling height). That file is imported into Rhino 5, where it shows up as an ellipse, also in mm. I’ve only been able to export it two ways - either as an oversimplified 5 segment polyline, or as a many many segmented polyline, neither of which is what I need - I just need it to come back as a simple ellipse.

I have varied the simplify tolerance between 10 and 0.00001 but get the 5 sided polyline every time. When I tick the curve tesselation box as well, I always get a 2D polyine with far too many segments.

From the help file, it looks like I should be able to export it so that it comes over as an ellipse (I can get circles and arcs to work fine, but not ellipses).

Any ideas please?



ExportedFromRhino - Too Simplified.dwg (14.9 KB) ExportedFromRhino - 2D Polyline.dwg (20.6 KB) Ellipse.3dm (204.1 KB) OriginalEllipse_R2004.dwg (263.7 KB)

Hi Jonnie.

To retain it as being a ‘true’ ellipse, change your AutoCAD Export Scheme so that on the curves tab, both ‘curves’ and ‘polycurves’ are set to “splines”.
This will affect ALL elements that you are saving to DWG - if it is only the ellipse that is fine, but you may have other elements in your drawing where a spline output is not preferable.
I have previously saved to DWG in two parts and then combined them in AutoCAD to keep preferred “polyline formatting”.

The alternate way is convert the ellipse in Rhino with Curve/Convert/Convert to Arcs where you can select min and max arc lengths. In AutoCAD you can draw a ‘true’ ellipse or a poly-ellipse which generally only has 16 arc segments.and is generally never noticed.
So a few tests with the maximum and minimum arc lengths should give a result that you are happy with.


Thanks Barry

I was hoping to be able round-trip the ellipses from CAD to Rhino and back, as it says ellipses are supported in the Rhino help for the AutoCAD export options, but it looks like they aren’t, so your polyline represesentation suggestion at the CAD end is going to be the best solution. Thanks for that.


That is incorrect. Ellipses are just special case spline curves. Try importing the attached dxf - a single ellipse exported from Rhino. It reimports into Rhino as an ellipse object. The export scheme used was 2004 Natural.

HTH, --Mitch

EllipseTest.dxf (162.4 KB)

It is correct, though, that Rhino doesn’t make objects that list as “Ellipse” in Acad. The Acad object is a Spline in the best case, as in Mitch’s file. The spline representation will come back into Rhino as an ellipse.
I’ll add that to the list to add to the Acad exporter.