On front viewport. Curve keeps drawing on z-axis. Help!

I have two lines (both flat on the c-plane in the Front Viewport). I am trying to connect them with a curve that would run diagonal along the x-axis and the y-axis. However, whenever I try to draw that connecting curve it goes inwards (that is, it moves along the z-axis).

This only occurs when I use a curve with multiple points to connect these two lines. If I just use a straight line to connect the two lines, it’s not a problem. Similarly, if I draw a curve unrelated to these two lines it’s also not a problem.

I notice that turning on planar seems to resolve the issue. Which is great but I’m hoping someone can explain to me what the situation I’m resolving actually is… that is, why is this curve going along the z-axis?

Any help would be much appreciated.

It sounds like the Front View CPlane is not where you think it is, hence any intermediate points would be on z=0, but your curves are not. A straight line snapping to your initial curves would be in the same plane as the curves, and also a multipoint curve would be with planar set to on. Try projecting your curves to the CPlane (in Front View) with ProjectToCPlane and see what happens. Or move your CPlane to the curves with Set Cplane to Object


Thanks very much.

Ya, you’re right. Setting the c-plane to the object resolves this. But setting the c-plane to the view (Front) or the even the Front World View, doesn’t resolve it. I would’ve thought the latter for certain would have fixed this. Any ideas why it didn’t?

One thing I noted is that this line came into creation when I traced (by snapping to the points) of a 3D object in the background. However, only certain parts of my traced object have this c-plane issue.

The only reason I can think of is that you have moved the CPlane away from the Front World position inadvertently, and then drew the curves on it. Set your coordinates window to “World” (right hand bottom corner), click on one of the curves, and read the y-coordinate. If your curve is on the Front World Cplane, it should read zero.


Edit: reading your additional comment, it is hard to trace back what actually happened. But in future when the result of any action shall be on the CPlane, be sure that your “Project” object snap is set to on.

Edit2: don’t just click on the curve, snap onto it (by starting a new curve for instance), then read the world Y coordinate.

When I click the problematic lines they show a y value of 27. So your diagnosis is correct. Also, thank you for the advice re the project o-snap. That seems to have resolved the issue, or at least allowed me to continue using the file.

One last question if you don’t mind… is there a simple way to snap the objects on the screen to the c-plane or do I have it backwards and am supposed to snap the plane to the objects (as per your original suggestion)?

If you start drawing a curve without snapping to anything, the start will be on the active CPlane. If you start the curve by snapping to something that is not on the CPlane, the start of the new curve won’t be either. If you then have Planar mode enabled, (and not snapping to anything else), all next points of the curve will be on the same z-elevation (relative to current CPlane) as the first point.

Then again, if you have the ‘Project’ Osnap enabled, snapping to non-z=0 geometry will still land your curve point on the CPlane. Hope that made sense…

Yes, this makes complete sense – but only to those it makes complete sense to.

To believe that any new user would know or easily understand how to do this would be a mistake. Much room for improvement here…

I believe that some things in life actually require ‘schooling’ (reading the manual, following tutorials, other types of training - or just asking questions to the peers in the community).

I also believe that most, if not all things in life can be improved. To state that is just so general that it is of no use at all. If you have a specific idea for improvement, by all means, spell it out.

I agree with your credo, @wim. Additionally, the third leg of my own philosophical triad is one of “perpetual improvement”.

Q: (In software) how does one know when there is a need for improvement?

A: When:

  1. There are oft repeated errors or confusion.
  2. Cumbersome or inconvenient requirements to do simple tasks.
  3. Complex explanations are required.

2D drawing in 3D space in Rhino meets all three of these criteria.

Do I have some specific ideas on this aspect? Sure. I, and others–usually mystified new users who are baffled by and not yet (ab)used to Rhinos methods on this topic–have mentioned a number of ideas over the years related to difficulties with the act drawing 2D drawing in 3D space and how this might be significantly improved. But in the absence of RMA recognizing the validity of these concerns–all aimed at making a very good product even better–these have been overlooked or dismissed.

Qualitative improvements are often not easy since they sometimes require re-examination of some “sacred” principles. Rhino items that would greatly benefit from a rethink are: CPlane, Project, Planar, Ortho, and Snaps.

I’m on a mobile device in Costa Rica and can not dredge up my frustrations and proposals for these items made over the years. Others could surely add better ideas if a concerted effort were made in this direction, I’m sure.

Good software has both Power and Grace. Rhino is immensely Powerful. My hope is for it to also become more Graceful.


It does. Thanks very much.

This should achieve that :smiley: