R7 DupBorder creating degree 3 curve (was degree 1 in R6)

Dear McNeel,

We noticed that DupBorder in R7 sometimes creates degree 3 curves from surfaces that are bounded by straight-line edges. in R6, the results would always be a degree 1 curve, i.e. a polyline.

In addition to the curves not being degree 1, DupBorder in R7 also adds 2 additional knots to every edge, at 1/3 and 2/3 the distance between the two corners. This happens from the Rhino command line, and also through rs.DuplicateSurfaceBorder()

When I run SimplifyCrv on such a border, the results is as expected, namely a closed polyline with the extra knots removed.

I am wondering why this is happening. Was this new behaviour deliberately introduced into R7, and why does DupBorder sometimes create tidy polylines, and sometimes it doesn’t?

Many thanks for looking into this.

dupborder_debug_R6.3dm (92.0 KB)


That’s odd.
I can duplicate the regression.
Added to the pile.

Thanks for the report and example.

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Hi Axel -

The link to that report is RH-68994. Can you provide more information about how that “bad” surface was created?

Hi Wim,
Both surfaces were created either with CurveBoolean, or by tracing the outline manually and running PlanarSrf. Either way, the input curves would have been polylines (degree 1). I’m afraid I am unable to provide any further details.

Hi -

Thanks, that’s fine. It looks like the cause for the change was found and we now “only” need to figure out how to reconcile conflicting expectations.

I just successfully tested the fix in what will be V7 SR 21.

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Thank you so much, John. Much appreciated