Blend Srf (G2) non-coplanar edges when input surfaces are?

Rhino
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1

I was modelling a tapered racetrack 3D form where the bowed sides have co-planar edges. However, after blending the rounded end surfaces I was surprised that the resultant polysurface would not cap. Turns out the blend surface edges where not coplanar with the input surfaces?

Below I’ve compared the BlendSrf output to BlendCrv outputs (which are planar).

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image2055×1643 186 KB

Using match surface to try and correct the problem didn’t work either.

The side surfaces are untrimmed lofted curves - that - when their ends are joined with straight lofts and joined will cap.

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image2020×1247 83.3 KB

2

Could you extend the blended surfaces and then trim them to be equal to the other surfaces for capping?—-Mark

3

Thanks for the suggestion Mark - there are plenty of ways I could work around this issue.

I’m reporting it as a bug since it’s not working as expected - If the input surface edges are co-planar - then the blend is not actually achieving G2 continuity (as I understand it) at the output surface edges if the resultant surface is not planar?

4

Odd, here it does.
Untitled.3dm (2.1 MB)

5

Hi Lagom, it’s fine when the input surfaces have no inherent curvature (like the extruded surfaces in your example) as the G2 curvature influence is the same as the G1 tangent influence (and therefore the blended surface edges remain planar).

My problem is when the input surfaces have curvature - see attached file.

BlendSrf_G2_edges_not_planar.3dm (3.2 MB)

In this instance the G2 (& G3 or G4) points start to roll upwards:

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image2175×1165 92.1 KB

6

I see. That is indeed odd, in view of the fact that BlendCrv builds planar curves, as expected. Also, the curves from BlendCrv come further forward along the x-axis, compared to the BlendSrf.

7

I should have added a 3 quarter view of the above image!:

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image1989×1360 102 KB