Make sketches timeless and the sketch elements timeline aware

[Anonymous]

I can't count how many times I needed to add something to a sketch and have visual reference of some bodies that disappeared because editing the sketch rolls back the History Marker.

For example, I create a body based on a sketch, than copy that body and move the copies. Then I want to keep editing the sketch while having an idea where the copies are. So I essentially have to make a new sketch in the same plane.

I know this is less likely to be an issue if you are modeling something that you have already drawn before and are just transferring it to CAD. But often times, I am doing the designing while modelling.

Having the sketch elements timeline aware instead of the whole sketch would allow for sketch editing without rolling the History Marker, while also preventing feedback loops in form of referring to future entities that refer back to the sketch.

[gman-r]

I don't think this makes sense to do. All objects in the history roll back the timeline to the point where they were created when edited. If your sketch was referencing geometry that either has has moved or is completely non-existent later in the history then the sketch would be totally broken. Also in the scenario you describe, you can get into some sort of inception scenarios where you create a sketch, extrude an object, create multiple copies of that object, or just modifications to the object and then edit the sketch again and try to reference those features. 

[Anonymous]

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@gman-r wrote:

If your sketch was referencing geometry that either has has moved or is completely non-existent later in the history then the sketch would be totally broken. Also in the scenario you describe, you can get into some sort of inception scenarios where you create a sketch, extrude an object, create multiple copies of that object, or just modifications to the object and then edit the sketch again and try to reference those features.

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Can you please elaborate how the sketch would be broken if the sketch elements were independent (time-wise) of the sketch itself?

These "inception" scenarios would not happen. Removing or modifying a referenced feature would have the same effect as it has now. Only it would allow you to reference not just past features, but also future features.

Think of it like this: As of now, you have to create a new sketch to reference a newly created body, even if the sketch elements you're about to create are tied to the same plane/face as some previously created sketches. What if the new sketch elements were created under the old sketch? Meaning a sketch is just a set of features that have common a common plane, like a folder of bodies. But the folder itself is not time-aware, it does not need to be.

[gman-r]

“ Only it would allow you to reference not just past features, but also future features.“

This is exactly my point. How can you reference future features in the past. The objects in the future are based sketches in the past. If you go to the sketch that describes how to generate an object and change it all future things that are based on it will change too so how could you reference those things. 

And also just think about it. If you align a few components then project some features from them on a sketch, wouldn't you want the objects to come back to the original position if you want to tweak something on the sketch? What if those objects don't exist in the future. What if they were just used as tool bodies? 

[Anonymous]

The idea is that you are not referencing future features in the past, because the sketch is not in the past, it is timeless.

When you edit a sketch feature that was used to create objects, of course it will change those objects. But if you reference those objects, the reference is a different sketch feature, which was created in different time . That's why I propose to make "the sketch elements timeline aware".

I'm not really understanding your second example, especially "wouldn't you want the objects to come back to the original position if you want to tweak something on the sketch". Regardless, any sketch feature (including projection) would be time-aware, so there would be no issues with past/future.

[gman-r]

The two points I was trying to make is:

1) Fusion is a parametric CAD software. The sketch profiles that are used to generate features are effectively parameters of the feature. The sketch must exist first to define the feature so temporally it is always in the past with respect to any features generated from it. The parametric nature of the system means that if you rewind history and change the properties of the sketch,  features that are dependent on it are re-computed based on the new properties. So any time you edit any object in the timeline, you really are returning back to that point in time. So for example, if you create a sketch and daw a circle which will be extrude as a hole. Imagine you decide to edit the sketch and change the diameter of the circle to be dependent on the profile of a chamfer that is later applied to that hole.  This would create a cycle in the dependency. Your updated sketch references the profile of the chamfer which itself depends on the diameter of the circle! There would be an infinite loop generating the hole from the sketch, applying a chamfer, which changes the projection which now cause the size of the hole to change again!

2) Sometimes you align objects a point in time specifically to reference them in a sketch to generate some other features. Generally you want the referenced projections to be linked such that if you decide to change one of the other objects, the sketch(and any dependent features) automatically reflect the changes.   In some cases those object are used for example cut a shape into another object. They may be discarded after the operation. If not for the fact they time is rewound when you edit the sketch, the referenced objects would not even exist anymore on subsequent edits which would make no sense. Or they exist, but they are not position the way they are required in order to generate the correct projection.  The point I'm making is that it makes no sense not to return things to way they were at the point the sketch was created when the sketch itself may be dependent on the state of the world at that point. 

For what you want to do, the simple solution is to create new sketch at the point in time that you want with all the objects that you want to reference positioned as you would like. If you need the second sketch to include features from the first sketch, that is perfectly fine, because you can always reference objects that already exist in the timeline.

[Anonymous]

@gman-r 

1) You are still not understanding it. The sketch would not be on the timeline. The circle would be. Perhaps as a grouped item together with other sketch features created at the same time . 

The example you give is not possible, because by editing the circle diameter, you are going back in time to where the circle was created.

2) Because of 1), this point is mute, the sketch cannot be dependent, the sketch features can be dependent. Referencing and projections would work the same way as they always did.

[gman-r]

I think we are just going back and forth at this point.  Maybe someone else can articulate it better. The bottom line is one of the main features of fusion and parametric cad systems like it is the history feature and dependency system. In fact it is the main reason I personally use the system. I have tried other smaller cad packages, but not having the ability to go back and revise my drawing and have it take effect in all dependent objects is a deal breaker for me.  The sketch is the way that you describe feature profiles  so not sure how the sketch could be excluded from the for the history and dependency and still accomplish that behavior.   But as you said, maybe I just don't understand.

[jahnj0584]

In solidworks, if a sketch is not a child of another feature, you can freely drag it around the history tree at will. See if fusion will do the same?

(but it is also strange of you to be sketching things off of later bodies)

[gman-r]

I’m pretty sure fusion also allows you to drag any object(including sketches) in the history as far back or forward as it can go without violating any dependency. 

[Anonymous]

That does not, however, solve the issue described in the original post.

[gman-r]

I think fusion has a way to turn on and off history at any point. Maybe when you stop capturing historythat will work more like what you would like to do. I have not tried it so not sure.