Sweep2 doesn't give G2

BlendSrf


Sweep2

MatchSrf

Results surprise…

Why the surprise? Different methods give different results because the algorithms are different.

Settings do not influence. The surface will remain on the computer (without printers).

Sweep2 + MatchSrf - result turns out more smooth - it is pleasant to me. However Sweep2 have a Curvature control, but result not absolutely G2. MatchSrf finishes continuity after Sweep2.
And my question - why so turns out?

Different commands use different methods for creating and modifying surfaces. That is by design. A skilled modeler learns about the differences and uses them to obtain the results they want.

You should never count on visual analysis, it is based on meshes as @Pascal already stated above, so you’ll get an approximation.

Sweep2 using G2 option will not give you the same accuracy as BlendSrf G2 does. If you want to see the difference, analyze geometry. Below is an example with 2000 tests per edge. Both surfaces have been matched at the section sides using the refine option.

Compare what Zebra shows at the dot marked with 0.15° and what Curvature Analysis shows at the dot marked with 0.0000053°. Use analysis mesh settings which are very dense.

analysis.3dm (4.7 MB)

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But how do you find out about them? Just pushing and studying.

I meant the analysis of Zebra - http://docs.mcneel.com/rhino/5/help/en-us/commands/zebra.htm
What analysis was used by you on a screenshot?

On what in general to rely when determining continuity between surfaces?
If tools give the approximate analysis whether it is possible to define quality on their basis?

On the surface geometry and the normal or tangent deviation at the joined edge. A simple example would be to project a curve on 2 surfaces (over the connecting edge) and explode the result to measure with GCon.

To some extend i rely on the visual analysis based on the analysis mesh too. But if i see strange results even with very dense mesh settings, i analyze the surface normals along the joined edge.

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I think it’s better to use Zebra - the analysis is always the right one.

How to analyze?

Eg. run _Line _Normal with the option IgnoreTrims=Yes, create a normal line for each surface joined at an edge. Both normal lines have the same start point. Then pre-select both lines and run the _Angle command.
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You can offset the 2 surfaces and then run Crvdeviation on the offset edges. This will give you the point where the normal angle deviates the most. You can also use trig to compute the angle.

Perhaps introducing a third control curve might help in your sweep 2 exercise. Try sectioning the top and front geometry by running a line from the mid point of each. Then blend the two curves using “curvature” as a control. I’ve posted my results for your perusal.

Robb, you are in fine form here tonight. Nice technique and I can see you have done this often on boat hardtops and especially those with those overhanging ‘brows’ or visors. I know what you mean in your suggestion but maybe you could show how you project the line to get the new blend curve to smooth out your surface generation.

see the attached…

see attached

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How could you receive this analysis? There is some tool?
2018-03-23_174748

@Modeler3D, using a python script.

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Ok.

@Robb, @davidcockey
I still am interested in such piece, at the indication of the different range (CurvatureAnalysis) the analysis seriously changes. How to specify the correct range in the analysis? What it is necessary to pay attention to?