Smooth Curves

Stamos · February 2016

Hello, I 'm learning Onshape. When I started modeling a vr-viewer, circles and curves looked smooth. Now after many sketches and features, curves are looking like polygons. Example (notice the top left corner and the lenses holes):
At the beginning

Image: https://us.v-cdn.net/5022071/uploads/editor/ul/bekon3g8rd71.png

At current state:

Image: https://us.v-cdn.net/5022071/uploads/editor/io/es0ocytnezs7.png

Am I doing something wrong? I'm not an experienced user but I did not have the same issue with Solidworks.

_Ðave_ · February 2016

You aren't doing anything wrong. This is just visual and Onshape is looking into ways of improving this.

-Dave_

Stamos · February 2016

Thank you.

øyvind_kaurstad · February 2016

Although purely visual, it is still really annoying, so I'm eagerly awaiting improvements from Onshape on this.

_Ðave_ · February 2016

+1 on awaiting improvements.

philip_thomas · February 2016

This is an ongoing project and internally we have gone through several algorithms for improving this. We have a longer term solution that is far more sophisticated, but in the meantime, look for a series of incremental improvements starting with the next release.

In the current release, because chordal deviation is per part studio (and depends on the total number of triangles in the part studio, regardless of whether the part is shown or not), you can derive one part into a new part studio and (especially in your case) there is a good chance that it will be at a higher resolution.

Here is an example;

Now derive that one part into a new part studio (for screenshots etc)

Don't forget that the (Free!) rendering apps also give you control over the chordal deviation (although i did not crank it up on this one

)

Also (as a reward for reading this far), here is a tease of the same dataset in the next release . . . . . .

Thank you for your support of Onshape and good luck with your project!

michał_1 · February 2016

brian_cook499 · March 2017

Has any progress been made with this? The low poly count is seriously hindering my ability to work on a particular model.
https://cad.onshape.com/documents/9efcb26f4bb0092bbbb2ea19/w/62e6909f1108465965aa4c36/e/fc64e4e5db2575c7b080f630

The two components have the same radius for the right side. They are actually a copy of one another with the bottom trimmed off on one.

Image: https://us.v-cdn.net/5022071/uploads/editor/71/yr0ottk61jmi.png

Yet as you can see below, even in a new workspace, they have different curves.

Image: https://us.v-cdn.net/5022071/uploads/editor/q2/tsx2za5755ha.png

As such I do not know if they are actually clipping through the surface of other components or if it is just a visual glitch.

Image: https://us.v-cdn.net/5022071/uploads/editor/9s/zkzjn8kp5x0z.png

Any help with this would be appreciated.

philip_thomas · March 2017

@brian_cook499.

Just to make sure i understand what you're asking, here is a restatement of what i think you want -
"I understand that as a purely graphical representation, Onshape parts will always appear slightly faceted - that said i need a way to generate images with smooth arcs (especially where the radius of those arcs is large)"
If that is the correct, then your best bet for a solution today is to use one of the many rendering apps available in the app store. Many include chordal and angular deviation controls as well as other methodologies for developing that type of images you are asking for.
I hope this helps

philip_thomas · March 2017

@brian_cook499 - i looked at your document and wanted to ask if you had made the conscious decision to build all the parts in single Part Studio for any specific reason?
During training, we state quite strongly that a Part Studio is used for building parts that have geometric relations between them. If there are no relations, the parts should be in separate Part Studios. This is purely for performance reasons (avoids re-generating a lot of features not related to the part you are trying to edit). Its a perfectly valid approach also to use a layout sketch in a Part Studio and build multiple related parts from that sketch, but all yours are laid flat so i dont think that was your strategy (BTW, a better way is to put the layout sketch in an assembly and then use In-Context across a number of part studios to develop the related parts - see the In-Context videos).

StephenG · March 2017

Could an Onshape expert provide a little more information about what determines display cordial deviation (tessellation) of surfaces for display purposes. From what I have read each Part Studio is treated uniquely and has it own tessellation settings.

Is this a mostly problem is when a Part Studio has a geometry mix of large and small radius of curvature surfaces, or is the amount of geometry in a Part Studio?

Evan · March 2017

@StephenG - you are correct: chordal tolerance is chosen on a part-studio level based on the bounds of the parts contained within. There is a limit placed on the tolerance to avoid spending too much time creating and sending the tessellation.

This tends to be more noticeable on parts with curves that have a large radius of curvature relative to the overall part size. The angular tolerance does not help much in this situation, and the chordal tolerance may not be fine enough to make up the difference.

michał_1 · March 2017

Hi guys, recently I've noticed some changes in tessellation, which I don't understand. I know I can expect some low-quality tessellation with large radiuses. I know that tessellation depends also on general size/complexity of design to keep good performance.

Now, I have this project: https://cad.onshape.com/documents/58d0eadf203be30fcdfff2c5/w/9436f156b05d9bd16bf49990/e/a923ab2cea1168d91bea12c5
It's a trivial design with just six parts but for a fairly small object, it's built with the use of large radius arcs. Until a certain point, I had no problem with how it was displayed. After adding last 8-10 features quality of tessellation dropped noticeably. I can't say if that was caused by these features or it was just correlated with some changes on your side.
Two weirdest things are, that I can rollback the bar and after rolling it forward step by step, quality of a tessellation improves:

Image: https://us.v-cdn.net/5022071/uploads/editor/ap/7aokmcgnavzi.gif

Second weirdness is that after that "step by step" method I can close my project and after reopening it's still fine, at least for some time.
To my understatement, Onshape doesn't store data for tessellated objects and recalculates whole feature tree each time we open design.
Before I'll propose an improvement I would like to know what I'm missing.

Evan · March 2017

@michał_1: Onshape minimizes the amount that we recalculate in order to reduce open times. So things like tessellation will be cached and will typically be available the next time you open your document. This saves the time it would take to regenerate the result of the whole feature tree each time you open.

Similarly, each time the your design changes (either through edits, or rollback/forward) we only recalculate what is necessary to reflect that change. So when you rollback a feature, only those bits of geometry that are affected by the feature will change. This is a nice efficiency, however it can lead to variation in results because the tessellator is considering only a portion of the model, rather than the whole. This is likely why you are getting different results as you roll back and forward.

That said, the magnitude of the visual impact you are seeing is rather large, and it warrants further investigation. I would encourage you to submit feedback through the feedback tool, which can be found under the "?" menu. This will help get the issue into our issue tracking system.

StephenG · March 2017

As much as Onshape tries to adjust tessellation during the modeling process to balance visual quality and performance it is never going to be able satisfy the subjective quality needs of every user.

Onshape I believe is completely in the dark when a user uses the mouse scroll wheel to zoom up close. If the geometry is a curved surface with a large radius of curvature you are going to see faceting. How much this "course" faceted display impedes the work flow is subjective; the data is there it is just not pretty.

What makes sense is to provide a mechanism to allow a user to request a re-tessellation of the just surfaces currently being shown in the graphic to addresses a user's display quality concerns. This new tessellation data does not have to be permanently saved in the Part Studio, let it be temporary to the browsing session.

(I appreciate the fact that Onshape does most of the work on the server side back end making it possible to run Onshape on almost any device anywhere that has a internet browser. I am curious about the possibility, if the client side has sufficient computing capacity, for Onshape to pass surface definition data and let the client do tessellation in a more dynamic manner. Going one step further, how about leveraging the power of an high end GPU to do the tessellation.)

Evan · March 2017

I agree that it will not always be possible for Onshape to predict the user's goal when they are visualizing their model. Sometimes they may prefer performance over precision. At other times, they may need finer precision. This does entail providing some means of user control. That said, we can also do better at finding a balance that works for most situations and most clients.

There is work that needs to be done to give the system the flexibility to do more automatic and manual level-of-detail switching. I can't say when the work will be complete, but it is definitely on our radar.

Stefan_DMS · June 2017

Has any further improvements been made on chordal deviation recently, some of our users are seeing assemblies with parts that appear as rough polygons rather than the round part they should be. Having a tough time trying to recreate the issue on my machine but definitely an issue for some users.

idesignstuff · July 2017

Seems like, if you know that this is a problem mostly for large radii, why don't they get tessellated at a higher quality(smaller chordal deviation) than small features with small radii?

Stefan_DMS · June 2018

Cheers, Love the new feature to fix tesselation.

mike_stanley · November 2019

Any updates on this? I defined a simple arc and it appears as a few straight segments. It's a 50 m radius curve. It makes it very difficult to work with when the approximation of a curve is so far away from the actual curve.

Image: https://us.v-cdn.net/5022071/uploads/editor/78/k24bupbl48op.png

NeilCooke · November 2019

@mike_stanley 3rd video
https://forum.onshape.com/discussion/9551/improvements-to-onshape-june-15th-2018/p1

Smooth Curves

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