displaying curvature graph on a curved (but flat) surface edge

Not sure I'm explaining this well, but how would I display the curvature for the curved (in 2d) edge of a surface that has 3d curvature in other places.

I've been dupedging then checking the graph, adjust original surface, then repeat. There must be a better way.

See attached sample image.

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dunno.. i don't think you can.. even if you subselect (ctrl-shift) the edge first then run the command, the curve will deselect itself..

So it's a trimmed edge I take it? A workaround might be to use history to project the curve onto the surface, not trimming it, and having the graph on while you edit the original.

It's not trimmed. Trimming isn't really a problem because I can see the curvature graph for the curve before trimming.


Hi Ryan- try this: make a plane, and with History on, Project the edge curve (not the duped edge, select the edge itself) to the plane. Turn on the graph for the projected curve and that will follow along with edits to the surface. Does that get at what you want?




Thanks Pascal. I admit I haven't really started to explore the possibilities with this feature. Is there any documentation? Not much in the help file.

Hi Ryan- are you referring to History? Yeah... we should probably have a brief overview of the feature as a whole someplace in Help- I am not seeing any so far. It might go something like this:

History allows the user to modify input geometry to a command to change the output generated by the command. If History is enabled for a command that can use History, then later modifications to the inputs will change the outputs. Edits to the outputs are allowed but break the history chain to the inputs. 

Example- ExtrudeCrv- make a circle, enable History recording and then Extrude the curve.


-move the circle- the extrusion will move as well

-turn on control points for the circle and move some around- the extrusion will change shape accordingly.

-Rebuild or ChangeDegree the circle- the extrsuion is modified


-select and move the extrusion- you get a warning about breaking History and subsequent changes to the circle are not reflected in the extrusion. Undo to restore History

- you can chain History- e.g. turn on History recording and then ExtrudeCrv or loft to another curve the top edge of the first extrusion- modifying the original circle will change both the first extrusion and the second surface made from its edge.

The thing to remember is- with History enabled for a command, editing the input objects  modifies the outputs.



Thanks Pascal.

A question came up while thinking through the implications of history... Does Rhino build up the history-enabled parts when you open the file? Or are the history parts stored as normal parts that are revised when the source parts are changed?

What I mean to ask is down the road open history parts in another 3d program from the original 3dm file? Or, fifteen years down the road, if Rhino changed substantially, is there any chance those parts of the model wouldn't open correctly?

Hi Ryan- the Rhino file contains the geometry as-is. The file also contains a history record of the History connections among objects that allows the History related changes to happen as needed. Not sure if that answers your question...



Yes it does. Thanks.

I like to think of History as Rhino's internal hidden form of Grasshopper.  Like Grasshopper, History flows one way, input to output.  Recursion is not allowed.  If you want a more powerful version of History in that the innards are exposed to the user take a look at Grasshopper.



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