[BUG] Loft edge not following simple profile.

[Anonymous]

After creating two rectangles with rounded corners, one slightly smaller than the other. I lofted from one profile to the next. This is the resulting edge of the loft.

Definite bug.

Still trying to generate geometry that doesn't cause a conflict.

[TrippyLighting]

Could you share your model ?

This article explains how to share a design. 

[AronGari]

I believe I have encountered the same issue as OP had. I have been designing a part that is over all rectangular with filleted corners, some irregular profiles, several transitions from a curve on profile 1 to a straight line on profile 2, as well as straight to straight profile. The part terminates at the plane that contains the loft profile sketches; however, the loft deviates from the profiles of both end similar to OP. Even using rails, I was unable to eliminate the deviation; it would only move from one part of the profile to another (maybe shrinking slightly).  In an effort to find the source of the error I was experiencing I produced a simple loft part that is rectangular with flitted corners. Here are some screen shots of the divination; it is generated with surface as well as solid lofts.

Oddly the deviation will disappear at a certain view distance. I am unsure if this is simple a rendering error or if the actual model geometry is changing.Here is a closeup of the deviation

Here is a link to the part https://a360.co/2CNh6vw. It contains two surface lofts one with fillets, and one with square corners; and three solids one with fillets (with rails), one with fillets (without rails), and one with square corners. As one last note the square cornered lofts accurately match the profiles; the only difference between them is the fillet.

Do we have to only add fillets post loft in order to get accurate lofts or is there something I am missing?

[AronGari]

I noticed something interesting after viewing the part in the web browser; the deviation seen in Fusion360 is not present in the browser. Which made me wonder even more if this is just a rendering error in the viewing window. So what I did was take the part into the the Render Workspace. With the Deviation clearly visible in the Render Workspace I ran a quick Standard Local Render. Here are the resultsRender Workspace view windowRendered Image

At this point I have to conclude that this is simple a bug with the view window rendering system. I will contact Autodesk support, and submit my findings to them.

[TrippyLighting]

This isn’t per se a bug. Fusion 360 uses a LOD (Level of Detail ) algorithm to reduce tesselation on objects further away from the camera in order to reduce data that needs to be processed. In Fusion 360 this happens on an object basis.

This sometimes leads to visible artifacts in the viewport. You can change this.

Find the component or body in the browser, right click on it and select “Display detail control”. Change it from Adaptive to Fixed/High.

This setting goes back to default (adaptive) each time you end your Fusion 360 session.

[AronGari]

I wouldn't imagine this is something most people will be aware of beforehand. I myself ended up spending greater part of two days trying everything I could think of (including redesigning my parts), and going through any forum posts I could find that might have a solution in order to figure out why my models weren't producing the intended geometry. I understand for some users the accuracy might not be of high importance for the models they are making. For me I used Solidworks for 9 years at my former employer, and have recently moved into freelance work now using Fusion 360 (that has required some adjustment). It is not an option for me to offer models that are inaccurate, or do not meet my customers design criteria to them; as I pride, and market my services as being able to offer both. For me accuracy is more important that speed (within reason); as in this case it cost me significantly more time having an inaccurately displayed model than what was gained by having the adaptive rendering. If the artifacts were produced in the opposite order (as in the model was less accurate as view distance is increased, and more accurate as the view distance is deceased) then this would be a non-issue IMHO.

Unless there are back-end reasons I am unaware of it would make sense to me to start with the high (or medium) detail accurate render and have the option to move to an adaptive render (as you make your part/assembly more complex) if need be. If it would cost too much time to resolve the artifact error caused by the LOD tessellation it would be nice to at least be able to choose the preferred global defaults in the global Preferences/Graphics tab; instead of being forced into the adaptive render by default.  At the very least a file wide "Display detail control" under the "Document Settings" tab in the design tree.

It seems somewhat redundant, but do I need to write up an Ideastation post about this?

[TrippyLighting]

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@AronGari wrote:

 If the artifacts were produced in the opposite order (as in the model was less accurate as view distance is increased, and more accurate as the view distance is deceased) then this would be a non-issue IMHO.

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The level of detail is in fact reduced as the objects distance from the camera increases.

In Fusion 360 (as I understand it) this is done on an object basis. That means one object has one level of detail. In objects with a high aspect ratio or a big difference in object size vs. model detail on that same object Fusion has to make a compromise.

I would agree that an easier way to set this maybe even permanently through the preferences or even on an object level would be great.

If you are concerned with the accuracy of your surfaces then I would also check out the Curvature Comb, Zebra Stipe and  Curvature Map tools.

BTW these also benefit from changing the display detail control level to fixed/high.

[AronGari]

What I meant by less or more accurate wasn't necessarily lower or higher detail, but trying to describe the appearance of the artifacts. Since they are only appearing close up in the high detail render, and not in the low detail one. If the artifacts only appeared in the low detail render it would be on non issue imo.

Thanks for pointing me to the curvature analysis tools; I must admit I have been slow in utilizing them. After this I will be making sure to spend more time working with them, and integrating them into my workflow.