Blend Surface Continuity Problem


The blend surface tool doesn’t seem to be achieving continuity between two surfaces. Although I select ‘curvature’ from the selection, it only seems to match the edges to position!

i tried in version 5 and it seems to work - although with a multispan surface.continuity issue.3dm (76.5 KB)

See attached.

If you tick “Interior Shapes” it seems to work. Looks like a bug to me though…

Perfect . That works.

I can’t understand why you need to check the interior shapes option…

Me neither, therefore the classification as bug :bug:

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Hi all - the InteriorShapes setting is a tough one to get right, and I’d agree that right now it is messy - in order for the ‘Simple’ (i.e. matching the structure of untrimmed inputs) style of blend to be possible, there have to be controls/shapes/handles at all these interior locations - but in many cases this is a very dense set of controls and not useful if you want the traditional (v5 style) blend surface with user-added controls only… Without them you can’t get the simple blend to have good continuity.

Here’s a thought - (@lowell … can you provide a sanity check? we might have already rejected this) The check box is called something like ‘Simple structure’ and ‘Add shapes’ is not available (grayed out), and moving the controls along the edges is not possible, with that checked…? In other words, there is no setting at which the continuity is compromised, is my idea…


The problem is that if you tick g2 continuity, you expect it to give you that, or give a meaningful error message. That does not happen, unless you tick interior shapes as well. To me, as a user that is unexpected behavior.

@Pascal -
I guess we rejected something like that a while back when we said that simple should happen automatically without a control to turn it on and off. That doesn’t mean we can’t unreject it though.

With your suggestion, would Simple be a manual toggle that would remember the last setting rather than come on every time simple is possible, but just be gray when it’s not possible?
Would Interior shapes be removed completely or would you still be able to turn the handles on and off for the interior shapes?


Hi Lowell-

I think that sounds right. If Simple is on, you must have all the handles (if I remember right that showing them is necessary to get good continuity)

One of the drawbacks now is there is not a way to get a shape change spread across the entire span along the edges and also get good continuity - that is, show no interior handles and modify the handles at one end and have the resulting shape blend or interpolate smoothly along the edges, and get good continuity. If I am right about that it seems like a step backwards.

I think there should not be a scenario where it is possible to get continuity less than what is asked for.

I’ll think some more, it’s good for me.


Two key points for me here as a user:

1 You’d expect to achieve the level of continuity specified by default. If it’s not possible, then there should be a message saying it’s not matching and to throw it in there, also the amount of deviation…

  1. The ability to retain the simple structure and to be able to adjust the shape at either end to achieve a smooth transition without having to deal with multiple interior shapes.

Also, are there plans to build continuity history with reporting - showing the level of continuity being achieved? With some sort of markers and maybe a single handle on the blend which allows you to knock the blend into the desired continuity.


Sorry about the paragraphs mixup! Two key points there.

I think there should not be a scenario where it is possible to get continuity less than what is asked for.

Exactly :slight_smile:

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Agree. Continuity less than asked for is a fundamental “fail” when blending or matching surfaces.

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