Mirrored curve has different G rating

I have a curve created from two views. I rebuild it and match it for tangency to an edge of an object. The G rating is then G1. However, when I mirror that curve to the other side is only G0. If I use match curve to make this tangent (G1) as well, will that make the mirrored curve no longer match exactly?

Are you talking about the continuity between the curves and the edge of your object? Maybe it’s the object that is not symmetrical…?


Much better to post the curves and the surface.


Here’s the model. I’m checking the fit between the object and the curves. I’m pretty sure the object is regular as it was cut from a single curve that was projected to a c plane.

Deoderant2.3dm (253.0 KB)

If you ask GCon about the curves and the edge of the surface, not the curve that is sitting there right on the edge, then both mirrored curves are G0 by the same amount, so to speak - 3+ degrees out of tangent.


The curve in the file along the edge is not symmetrical. Grab the curve, move it up in front view vertically to see better. Then cut it in half along the Y axis in the front view, and mirror one half over the other. You will see a difference at the end.

Okay, I think what you’re referring to is the curve that was projected to the c-plane. Is there a modeling setting that would make for more precise modeling? That curve was taken from edges extracted from the central object that had been trimmed with a line on the perpendicular c-plane. Is there something I’m failing to do in the process?

It seem I’m selecting a curve on one side and an edge on the other?

I’ve attached a series of shots to show the process in which I end up with a non symmetrical curve. As far as I can understand the curve should be symmetrical. Is there something I’m doing wrong here?

Just a suggestion, it would be easier if you posted your screenshots in the post, that way we can see them all by scrolling and not having to open each one in a new browser tab.
If you don’t know, Shift+Command+4 lets you take a screenshot of a selected area. Then just drag & drop from Finder to this area.
You can also use QuickTime to so a Screen Recording and upload the MOV file.

FWIW - not helping with the curve issue though. I am not sure what you are trying to do. Should the blue be separate from the red? Are the curves used for cutting?

Maybe post your model as well, It helps to see where the issue is. Try cutting your model in half and mirroring it, if it is not symmetrical .

Will do. Sorry for the hassle. I’m using a line to cut through an object made by extending a circle so it should be symmetrical to begin with. Right? However when I then duplicate the cut edge it’s apparently not symmetrical.

Deoderant2.3dm (421.7 KB)

No worries, just suggesting ways to get better feedback.

It depends on if the original circle was planar.

I will have a look tomorrow.

Rudi, did you have a chance to look at the model yet?

I did this morning and from what I remember, just getting home from a day doing other Rhino, is needing to know the original curves you used to run the CurveFrom2Views in your original post. If they are in the file, I have it here and can look in a bit. Are they on the layer OLD CURVES ?

This one

or this one,

Just getting my brain back into this model.

I believe it is just the way you are modelling and without looking over your shoulder, it is hard too tell you how I would do it “my way”. It comes with experience and practise.

Are you using ortho, or spacebar to constrain your mirrored objet position? Is the difference of G rating going to affect your final outcome? Sometime we have to remember not to sweat the small stuff.

If it is understanding workflow and technique, there are some good courses by Infinite Skills, Polyplane and I believe Lynda dot com has one. There is a book on Rhino5. Most of those are Windows based, but it helps build good practises, I am trying to get good workflows myself, because i am mostly self taught.

Best of luck and keep the questions coming, this is great software and there are great people on this forum who like to help out.

Yes all the curves used are on the curves layer.

Most of the curves look fine, finish the model and then check the surfaces if you need to, with zebra.

Well. that’s the rub. I can’t finish the model because I keeping hanging on this problem. I’ve rebuilt the model from the images up several times and I keep getting bad surface matches. What settings do you use pertaining to the absolute and relative measurement derees? The default is (metric) absolute tolerance.001 / relative tolerance 0.1 / angle tolerance 1.0 degrees. Is that suitable?

Is it between your blue & red Portions? If so, I will try to build it tomorrow morning from your curves. I have your screen shots to go by, then I can probably give you a better workflow on how to make an odd shaped bottle / container. Off for the night!

Not getting into tolerance settings, I just leave mine at default. I took your existing curves and rebuilt one to make it target to existing edge. Your curves are no good here. Check layers.

Mirrored it and split front curve at blue object edge. Circle 3 points at bottom, split at side curves and duplicated the blue object front edges & joined. Surface from network curves, choosing top nd bottom curves then 3 vertical curves.

curves to blue surface edge are both G1.

Deoderant2 Revision1.3dm (568.2 KB)