A Question about Base Features

[nnikbin]

It seems that during the creation or editing of Base Features, other objects outside of the current Base Feature will become read-only. For example you will not be able to delete, clone or split existing objects when creating a new Base Feature. You can only modify the objects that are created in the current Base Feature.

What is the reason behind this behavior? Is there any way to modify existing objects during creation of new Base Features?

[TrippyLighting]

This little section in the documentation explains the purpose of a base feature.

In s\essence it allows you to model geometry in an isolated direct modeling environment within a design that does have a timeline.

I just tried it pouted cannot reproduce what you describe. Can you share your design or create a screencast ?

[nnikbin]

Hi @TrippyLighting,

Thanks for your reply. Suppose you want to edit an already existing model using the Base Feature direct editing. It seems it is not possible unless the creation of the model be part of the Base Feature.

Please follow the following steps:

1- Create > Sphere

2- Create > Create Base Feature

3- Modify > Split Body

It will not be possible to select the sphere as the "Body to Split" in Split Body command dialog

[TrippyLighting]

You need to create the sphere within the base feature, so after you create the base feature.

[nnikbin]

Hi @TrippyLighting,

Thanks for your reply.

So I return to my original questions:

1- What is the reason behind this behavior?

2- Is there any way to modify existing objects during creation of new Base Features? by "Existing Objects" I mean the objects that are already exist before the creation of new Base Feature.

It seems that the answer to my second question is: "No, there is no way to modify existing objects during creation of new Base Features."

So, what is the answer to my first question? Is this behavior the result of some technical constraints or this it is just "By Design"?

[TrippyLighting]

I'd have refer to @jeff_strater for the ultimate answer, but I would say that this is by design. It makes little sense to try to modify geometry outside of the base feature from within the base feature.

If you want to modify that geometry then simply finish the base feature.

If you have a specific use case where you feel that this would be useful, then please post it. It would help to support the case.

[nnikbin]

Hi @TrippyLighting,

Many thanks for your reply.

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If you have a specific use case where you feel that this would be useful, then please post it. It would help to support the case.

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The main reason I want to modify geometry outside of the base feature from within the base feature is performance.

I'm developing an add-in which modifies bodies by performing hundreds of commands. I think using Base Feature without the overhead of timeline, parametrics, ... will increase the performance of operations.

To increase the performance I can not use TemporaryBRepManager because some operations that I need to perform are not available in TemporaryBRepManager.

In addition, users of my add-in do not benefit from the inner mechanism of my add-in. Using Base Features hides the unnecessary details from the users.

[HughesTooling]

If you copy the body before creating a base feature you can paste it into the base feature after it's active or you could use boundary fill to create a copy from within the base feature. The other option is convert to DM feature to convert a body to a base feature but either way you are not going to be able to edit a body that still has features in the timeline from inside a base feature.

Mark

[jeff_strater · Accepted solution]

I can explain a bit about the nature of Base Feature, its limitations, and its intended usage.

Fusion supports two very different design types:  Parametric Design (history-based), and Direct Modeling Design (non-history-based).  Parametric designs have a timeline across the bottom, which is a linear series of features.  These designs allow you to go back in time, edit earlier features, and have the model recompute.  Parametric modeling is powerful, but also complex to use.  Direct models, on the other hand, have no feature timeline (there is no connection between a sketch and an extrude in a direct model).  They are more flexible, but also limited in what you can do, if you want to edit the design later.  More info here: direct vs parametric

Rather than have these as two distinct and non-intersecting worlds, we decided to try to create a more hybrid design type:  Base Feature allows you to embed Direct Modeling bodies within a Parametric design.  Think of a Base Feature as being similar to a Form/Sculpt feature - it's a self-contained "island of direct modeling" within the larger design timeline of the parametric design.  When you edit a Base Feature, your design scope is limited to bodies (and sketches and work features) that are inside this island.  It's very modal.  Edit the Base Feature, do some direct modeling there, then exit back to your main parametric design scope.

Why is the design scope in Base Feature limited to the objects owned by that Base Feature?  Because it has to be.  To use @nnikbin's example:

1- Create > Sphere

2- Create > Create Base Feature

3- Modify > Split Body (want to split the Sphere)

Remember, while editing a Base Feature, no timeline entries are created, so if Fusion allowed this Split Body to occur on a parametric body, any update to features before the Base Feature would cause that operation to be ignored.  To carry this example forward, say this Split was allowed.  After exiting the Base Feature mode, you would have two hemispherical bodies.  Now, say you filleted the edge of only one of those hemispheres, which creates a Fillet feature in the Timeline.  So far, so good.  But, remember, the Split Body is not a feature in the Timeline.  It was created during a Base Feature (direct modeling) edit, so was not captured.  Now, say you go back and edit the Sphere in step 1 to be larger.  The Sphere recalculates, and is now bigger.  But, the Split was not captured, so it never happens, the edge that you filleted no longer exists, and fails.

Hope this helps clarify the behavior, at least somewhat

Jeff

[nnikbin]

Hi @jeff_strater,

Many thanks for your detailed explanation.

[nnikbin]

Hi @HughesTooling,

Thanks for your reply and for your suggestions.

[alexander.tatevyan]

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@jeff_strater wrote:

When you edit a Base Feature, your design scope is limited to bodies (and sketches and work features) that are inside this island.

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Hi Jeff.

I experience slightly different behavior.

Let's say I created BF1 and put a sketch inside it, made an extrusion from it, finished the BF1, then created another BF2, put a sketch there, made an extrusion, finished BF2.

Now, if I edit BF2, I can still see both sketches available in the browser and ready for editing, and I can even use the sketch of BF1 to extrude another body from it, if I like to, which will then belong to BF2. Now, for the bodies, just as you described, I can see all the bodies in the workspace, however only the body owned by BF2 is listed in browser and available for modification. To get access to other body, I need to finish the BF2 and edit BF1.

So, could you please confirm, that it is by design, that all the sketches, created in either of previous BFs, are always available for editing when you enter more recent BF on the timeline? Because, currently, the behavior I experience is not consistent with your statement, IMO.

Also, is there a way to tell which objects belong to which BF without entering the BF?

[jeff_strater]

I'll start with the last question first:  "Also, is there a way to tell which objects belong to which BF without entering the BF?".  That answer, unfortunately, is "no".  This is one bad thing about base features in Fusion.  It's even worse - you cannot tell which sketches and work geometry are owned by a base feature vs being parametric.  It is a source of confusion, definitely.

And, yes, I can verify the behavior you are describing:  If you edit base feature N, then any sketches owned by base features 1 - N-1 seem to be editable.  Any sketches from N+1 or beyond are not editable, simply because they have been rolled out by the base feature edit.  I would say that is a bug, not intended behavior.  At least, I cannot remember, or come up with a reason why this is desirable.

The truth is:  Not too many people use base feature.  I think it has its place, but it is definitely not widely used.  So, for better or worse, I don't expect these relatively minor issues to get addressed any time soon.

[alexander.tatevyan]

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@jeff_strater wrote:

I'll start with the last question first:  "Also, is there a way to tell which objects belong to which BF without entering the BF?".  That answer, unfortunately, is "no".

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I later discovered, that at least for the bodies, when you select them, you get this 'floor marking' over the BF in the timeline, which clearly indicates, that the body(s) belong to that very BF. Something is better than nothing 🙂

This, however doesn't work for the sketches.

Few more observations (just for fun, nothing critical):

1. When in BF edit mode, if you apply features, like Extrude, Fillet, Hole, they all appear as a list in browser. However, if I apply Offset Face, it never appears there. Is this also a bug?
2. If I create a BF, a circle sketch inside it, and extrude it to a cylinder, finish BF, then select the top face of the cylinder outside of BF, and create another extrusion from it with Join operation, the body then seems to convert to parametric one, and the extrusion feature now appears on the timeline. If I then select the body from workspace, the 'floor marking' hovers over the last extrusion feature on timeline, however, if I select the same body from the browser, then the 'floor marking' now points to the BF. This causes a confusion as whether to treat the body as parametric or directly modeled.