Troubles with understanding cplane

I have used a cplane that I created on another project but never felt quite comfortable that I really understood. In this current project New-Tomi-Railing-1220sep.3dm (65.5 KB) I have set a cplane between the vertical red line on the first step and second step by setting the origin and direction of the axis. I thought that if I had set the cplane to that space and if I then tried drawing a freeform curve in that plane, then my line would stay in that plane. Somehow it doesn’t. No matter whether I have Planar set or not. I’ll start a line in the front view and as I draw I note that it is going strange places in the top view and perspective view. Then I have to go to the top view and used the control points to drag it more or less into the plane that I want. I am either missing something or not understanding something about cplanes. I did go back and work through an earlier tutorial I had about cplanes and thought I understood. But that was a simple example setting it to an object. What am I missing? Should I create a surface between those posts and then set the cplane to that surface?

CPlanes are per-viewport - only curves drawn in the viewport where the custom CPlane is active will end up on that plane - as long as not snapped to something else.

So if I set the Cplane in a viewport, it is only active in that viewport? One of the problems I’ve had with Cplanes is knowing (remembering) which one I’m in. There doesn’t seem to be any indication except how the viewport looks if you’ve set something askew of the normal world.
Seems to me that a good feature for Rhino7 would be to have an option to set all viewports to the same Cplane. Yes? No?

No, not really. Imagine that you set the Top CPlane in the Front and Right viewports. You wouldn’t be able to draw anything in either as you are looking at the CPlane edge-on…

You can try setting “Universal CPlanes” in Options>Modeling Aids. If you then set a custom CPlane in the Perspective viewport (the only one I recommend doing this with), the world Top/Front/Right viewports will change to be the Top/Front/Right Views/CPlanes relative to the CPlane set in the Perspective viewport.

I find this to be too confusing for my liking however - YMMV.

Rhino is confusing because it is easy to forget which construction plane is active. OneView command eliminates the confusion as long as all the construction planes are orthogonal (mutually perpendicular). SynchronizeCPlanes command also helps - if you forgot which construction plane is active, use the SynchronizeCPlanes command. In my opinion, the NamedCPlane command should be integrated with the CPlane command and with the Rhino interface.

In my opinion, Rhino can be confusing because of all the “hidden” commands. When I went to the help website and typed in Cplanes I don’t remember seeing any of these other things like SynchronizeCPlanes. I won’t use these on this current project because I’ve managed to get my lines the way I want this time. But it sounds like I should start a new play project when I have time and try these things on something that doesn’t matter so much.
I think an entire book might be written on Cplanes.
Thanks much for the suggestions.

You might be right, it’s one of the least-understood concepts by new users in Rhino.

SynchronizeCPlanes is like a one-shot “Universal CPlane” operation that is not persistent. Even more confusing IMO.

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I am the opposite. I use Universal CPlanes and find Standard CPlanes confusing. When using Universal CPlanes the origin of the viewport coordinates sytems is the same in every viewport, viewports and the viewport coordinate systems remain orthogonal to each other. With Universal CPlanes setting a custom CPlane is equivalent to a change in model coordinate system.

When using Standard CPlanes the origin of one viewport coordinate system is different, and one of the viewport coordinates systems may be not orthogonal to the other two if the new CPlane is not orthogonal to the other two CPlanes. That can be confusing as I tend to move between viewports.

One method of working where Standard CPlanes would make sense for me is if a new floating viewport is created and then given a unique CPlane for work in that new viewport only.

I definitely want to try the Universal CPlanes in an experimental project to see if they will work for me. I have found in my shop that my working tools and space have evolved as I find the kinds of jobs I like to do. It is the same with drawing, no one method will fit all. I just wish someone at McNeel would write a tutorial paper that concentrates on CPlanes and the varieties thereof. The little tutorial that I have that is contained in a beginner’s tutorial of how to draw with Rhino is not enough. Tutorial videos don’t work for me where Rhino is concerned.

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I’m with Mitch on Universal vs Standard - somehow I always like to relate back to World xyz in my so-called mind, to stay oriented, and I find that I can do that (more) easily if I explicitly set a custom cplane in the view I’m interested in at the moment and keep the others standard.