Error in exporting hatches to .DWG

In the attached 3dm file, export all the objects to a DWG using the “2004 natural” option. Re-open in Rhino and look at the small black hatches (circle fills), they should be fine, nice and round.

Now, export again, but in the export options UNCHECK the curve tesselation parameters before exporting. Now open the new export file in Rhino and examine the circular hatches. They are very badly faceted… The circles that made the hatches are still fine. IMO this should not be happening…

Thx, --Mitch

BadDWGHatchExport.3dm(230.8 KB)

Thanks, Mitch- checking it.
Bug track item:
these are not visible to the public, yet.

I know that this post is old, but is there a solution to resolve this issue while exporting hatch? <
I have the exact same problem with circular and smooth curvy hatch contours in Rhino 6. They all get messy and polygonal after the export.



I don’t see any resolution in the above cited bug report, it appears to be still marked as ‘future’. So maybe this just got forgotten. I guess the workaround is to make sure the curve tessellation parameters are checked.

Hi Quentin -

RH-21803 is still open. From the original report by Mitch, it looks like that the factory-default 2004 natural export scheme worked fine. Did you try that?

I just checked in both V6 and V7 2007 Natural without the tessellation parameters being checked - and the problem is indeed still there. So no, it has not been fixed yet.

Hey Mitch - I wasn’t saying that it had been fixed. I made that item visible to the public and reported that it was still open. I didn’t check any of this but from your original post…

… I inferred that the default “2004 natural” option correctly exported the hatches. I might be reading that wrongly…
At any rate, there even isn’t a “2004 natural” option in either Rhino 6 or 7 so I probably shouldn’t have suggested trying that.

The main takeaway is that unchecking the tessellation parameters checkbox causes this, whether it be DWG 2004 from V5 or 2007 from V6 or V7. The default 'Natural" flavor has this box checked, that’s why the problem doesn’t happen. You have to modify the default setting to see the problem.

Yep, couldn’t find any solution. Even the problem does not appear a lot on the internet.

My only workaround was - as Mitch is saying - to use the curve tesselation parameters at the export. But doing this, the spline/curvy hatch contour are changed to polylines.

There is really no way to keep them as they are on the rhino file?

I hope this get fixed soon, or at least one day.


No, this is not actually the case. Spline curves are unaffected - as long as you have “export curves as splines” set:



Export settings:

I have the same issue. When attempting to export hatches in DWG or DXF with tessellation active and “export curves as splines,” the hatches are converted to polylines. It doesn’t match what Mitch explained. How is this possible?

I am using Rhino for Mac.
Thanks for your help


Reimport without Tesselation:

Reimport with Tesselation:

Dunno, just did another test in V8 (but PC not Mac) and splines plus hatches are not tessellated on export with those settings. There is no tessellation done on import in any case.

Can you post the .3dm file you used to test?

Hi Mitch, thank you for your response. Here is the file, containing the original hatch and an import from an Acad 2007 natural export.

Finally, my goal is simply to export hatches with smooth splines.

3DM_Hatch export.3dm (3.5 MB)

OK, I think I understand what you are seeing. The original hatches were made from smooth curves and Rhino “remembers” those curves so that if you run DupBorder on them, you get the original curves back.

But in fact, hatches in Rhino are actually sort of meshes internally. The hatches are quite finely tessellated, but the tessellations are there and you can see them if you zoom in far enough. This is on your original hatch after I duped the border (red).

You can see the tessellation on the hatch edge, but despite this fact, dup border is a NURBS curve and not a polyline. So Rhino is sorta pulling the wool over your eyes.

However, when you export the hatch, the internal info that Rhino has on the border is lost. If you re-import it and dup the border, you will get the “real” polyline edge and not the original curve that made the hatch.

Thank you for your explanation. It explains very well how it works and its consequences. I will then work with it for now.

However, it would be really nice to have hatches with smooth curves. This could improve compatibility between software, particularly for those that allow you to simply fill a closed curve.

Or a way to export hatches like this, Rhino has the information somewhere as it is able to extract smooth curves from them. An alternative that could already help, would be an option to export hatches as closed curves only. (It would be like a DupBorder included in the export.)