MoveExtractedIsocurve does not work in Rhino 7.8

I use ExtractIsocurve command first to make a curve. Then I try to move it with MoveExtractedIsocurve command. The MoveExtractedIsocurve command does not work because it cannot select the curve. By the way, the ExtractIsocurve command automatically turns off History. (The MoveExtractedIsocurve command works well in Rhino 6.34.)

Hi Andrew -

I’m not seeing that part here - when I simply click the Record History button on the status bar and then run ExtractIsocurve, the history recording is turned off as expected (a single-shot recording). When I right-click the button and pick Always Record History, running ExtractIsocurve does not turn this off. Are you doing something differently?

The way this command works appears to have been changed and this change is reflected in the help file: Rhinoceros Help
Apparently, history must be enabled when running ExtractIsocurve for this command to work in Rhino 7.

In v6, the MoveExtractedIsocurve command allows picking ANY curves (this could be a problem?), not just the curves extracted by the ExtractIsocurve command with/without history. If the curve does not have history recorded, the MoveExtractedIsocurve command asks for picking the base surface and re-link the curve to the surface. This may give a wrong impression that the ExtractIsocurve command in v6 always records history. So you think the ExtractIsocurve command in v7 turns off history.

In v7, RH-62420 made the MoveExtractedIsocurve command highlight all the curves extracted by the ExtractIsocurve command with history. Other curves cannot be selected. the MoveExtractedIsocurve command won’t re-link a curve to a surface. Maybe @mikko can explain why?

Yes It works as you described it in Rhino 7, but there are four problems:

  1. These commands are documented here: Rhino - Bongo - Animation for Designers, not here: Rhinoceros Help
  2. Documentation of History command is here: Rhino - Bongo - Animation for Designers It does not mention the fact that History is turned off automatically after every command.
  3. Documentation does not mention Always Record History option.
  4. Documentation does not say that History must be permanently turned on before starting the ExtractIsocurve command.

By the way, Rhino document search website does not work - any search is endess loop. This website is here: Rhinoceros Help

@andrew.nowicki the help search just quit working (along with random redirects to the Bongo page). Hopefully they will have it fixed soon.

We never had these problems with the old forum. It was posted here:

I see some bugs about the Bongo website and redirect that were fixed a few hours ago. Is it still a problem?

I did not know that MoveExtractedIsocurve was a command until reading this thread. It is always possible to read something. What is a typical situation where this command is useful?

RH-33512 added the MoveExtractedIsocurve command, but no more information can be found. This is what I can think of, working with ArrayCrvOnSrf + History.

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Help docs appear fixed now.

It’s one of my favorite commands when form-finding. I pull an isocurve and get both a base target crv + srf with _Flow. Then edit the base srf and move the iso till I get the right pattern.

I use it a lot for creating a patch srf between two srfs. I’ll snap iso’s on the two srfs, create a _BlendCrv between the isos, and adjust them as needed. It’s also nice for solving a 5 sided srf.

There’s even a mock subd workflow where I take a straight sections loft, extract isos, and loft loose through the isos. Then you can slide the iso’s to sharpen or loosen corners.


A server problem that has been fixed.

That is the topic of the History command. Record=Yes is permanent. You are talking about clicking the “Record History” pane on the status bar. I’ll add some notes to the “Steps” section.

You don’t have to. You can click the Record History pane to only record history for the next ExtractIsocurve command session.

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Shouldn’t be an option instead of a proper tool?
I mean that MoveExtractedIsocurve should be an edit option into extractisocrv tool.
It would be simpler and more coherent with others tools.

You are correct. (I tested it before posting, but I got it wrong.)

@wim There is another problem - if I turn on history temporarily or permanently before the ExtractIsocurve command, there is no way to delete the isocurve. I tested this bug in a new file made without template, I ran HistoryPurge command, and I still cannot delete the isocurve, but I can move it with the MoveExtractedIsocurve command. I can delete it after turning off Lock Children.

No No (Discourse rejects single No.)

Hi -

That sounds like you have the Lock Children option enabled.

I can’t reproduce that here.

I mentioned it in my last post. By the way, Rhino documentation says: “The HistoryPurge command removes history from an object and its children.” This sentence includes all children, including all locked children.

You added that after I answered, yes.

Correct, and not being able to delete if after purging is something that I still cannot reproduce here.


“The HistoryPurge command removes history from an object and its children.”

That probably needs updating. It breaks a selected obj’s relationship with the parent and leaves the obj’s relationship with its children intact.

“Select the All option to remove history data from every object in the model.”

This is also very curious. _HistoryPurge All affects every obj in the file while _HistoryUpdate All follows the traditional definition of “all” meaning “all selectable” (i.e. _SelAll). That feels completely backward and explains why I avoid both purge and update.

In terms of exceptions to the rule, purge is completely undoable. I have been burned by purge enough that I made a button to replace it.

And I also don’t turn off update children, because _HistoryUpdate All doesn’t behave like _History Update=Yes does. Locked/hidden objs are excluded from the update. On a complicated model with nested hidden layers, it’s a PITA to work with.

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This looks like a bug. You can see the command reports how many objects are updated, the number includes locked and hidden objects. Reported as RH-65232, and it’s been fixed.


@davidcockey - I use it mostly with a History enabled MatchSrf, with CurveNearSurface=On - that way, I can slide the isocurve around and the matched surface will follow.