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Arc / Circle / Curve Segmentation in Sketches
don_williams909
Member Posts: 142 PRO
in General
Is anything ever going to be done to improve resolution of arcs, in both sketches and models? Yes, I know, zoom in and eventually a curved part will stop looking like it has a bunch of choppy looking edges.
But not in sketches.
The segmentation of arcs just cost my company a lot of money because the designer who designed a part for us in Onshape couldn't tell that two arcs from two parts were actually intersecting and not tangent or creating a clearance between the moving parts. Now we have to have 125 parts remade.
This poor screen resolution has got to stop, and we need a curve to look like a curve in a sketch.
The segmentation of arcs just cost my company a lot of money because the designer who designed a part for us in Onshape couldn't tell that two arcs from two parts were actually intersecting and not tangent or creating a clearance between the moving parts. Now we have to have 125 parts remade.
This poor screen resolution has got to stop, and we need a curve to look like a curve in a sketch.
If the online-based CAD software can't create the bandwidth to show true graphic representation, then I'm sure that many of us would conclude that it simply can't keep up with installed-based software.
This is too important to ignore any longer.
2
Comments
If you are still having problems viewing a decent resolution than the problem is your computer. On a day-to-day basis I hardly ever see segmentation even on large drawings.
Go to system check in the "?" Menu and take a screenshot so we can take a look and rule that out
That's odd, usually the sketches are much smoother than the model.
Can you show an example? How much detail is in the sketch?
Should the designer be making parts by eye? I would take 125 parts from his pay 😉
It's not readily apparent if these two arcs are tangent or interfering, except that I added the center lines which might indicate that they are interfering.
HWM-Water Ltd
Have a look at the sketch called "Left" and zoom in at the top of the sketch. It was difficult to constrain my because where the sketch geometry should be, is not where Onshape displays it.
https://cad.onshape.com/documents/f117870c7911e20bd0f5ca85/w/92859ff0d8ddd004afac131e/e/d4a615d87b73c270fe9b853b
I just changed the tessellation quality of the parts to very fine following the advice in this thread, which made the parts themselves look a lot better, but the main issue is really with how coarse the sketch geometry displays.
https://cad.onshape.com/documents/5c81a571f71fc3a99e3618a5/w/529996ec624ec76bec7f3570/e/1b3805724794a95af24cd737
Might have figured it out here?
https://www.onshape.com/support
"This is purely a graphics issue as the arcs are not tessellated with a high enough quality to match the part."
Obviously this response is accurate but how is this even remotely possible in a program like Onshape? How would it even be possible to model an example like one posted above by david_van_der_meer with segmentation as it now exists? Has this issue never come up before? And not addressed yesterday?
The design I linked to in my earlier comment was my first attempt to model one of the most simple designs in our organisation, with the intention to take this example to the design group to discuss suitability of Onshape in the production environment. You need to come well prepared and show how well it can work, otherwise you will end up being told how much better SolidWorks/Inventor/AutoCAD is.
Instead, despite the overall simplicity of the design, I realised I could not go to them with this and present Onshape as a usable solution to them, as I struggled to accurately constrain this geometry.
After changing the tessellation to fine, I've now found there are material clashes in the model I couldn't see earlier, caused by me not being able to apply the correct constraints in the sketch.
I can understand this behaviour would be required for performance, but you would expect some kind of auto-refine (or even a manual "regen" in AutoCAD speak) as you move in closer to the area you are working on.
The trouble for me was that after adding a tangent line to my curve, I wouldn't be able to tell which line was the "curve" and which was the tangent. It didn't prevent me from doing anything, but was definitely annoying. I had to highlight the constraints to show which of the elements were actually coincident.
Which just proves that Onshape isn't probably willing to increase the tessellation of the sketch entities because it uses way too much graphics processing power to do it, and it would probably slow their system down radically. Notice that they side-stepped the question with their answer?
They didn't say that they can or are willing to increase the tessellation quality, just that it's not "high enough quality to match the part."
The fact they messed up your parts just because of tessellation means they have no clue how computer graphics work. A drawing that has a leader that has a proper radius callout goes a long way. Especially when you get a non-cad user that is muddling his way through it, and doesn't understand how computer graphics work. That and drawings tend to have finer detail when printed than some shop guy's old hand-me-down PC.
So in the end, it is the fault of your detailer (or lack there of). Sorry not sorry, you do half a job and you got half a part.
These are completely different scenarios and I completely agree that the first scenario is a legitimate concern (especially without native interference/collision detection). I haven't run into issues with clearances, but I have had difficulty selecting the appropriate entities which is annoying at best.
If the clearance was that tight, there is no doubt there should have been a double/tripple check. We all F*&% up now and again. But own up to your mistakes.
tessellation 'should' be a well known issue for any computer graphics professional. It is annoying, but that's about it. "It's a poor craftsman who blames his tools"
The parts were made to print. The prints were detailed properly.
The problem was that the lack of proper arc detail caused the Engineer to not realize that there was a very slight interference in the design. This part rotates, and it was supposed to just clear the other part, but instead it hit it, and was unable to lock into place properly. There was virtually no way to tell that from the poor tessellation in the sketch. Even if he had tried to create some test geometry, again, the tessellation would prohibit that from working. Yes, he probably could have found another way to detect the issue, but the reality is that poor tessellation was the major contributor to the design error.
I've used other CAD software where sketches had none of these issues. The case for having dedicated CAD workstations with proper graphics cards and installed CAD software becomes stronger than having a web-based software that simply can't provide the same level of graphics quality. Onshape has many wonderful qualities about it, most notably, their customer support team, but there are some serious shortcomings as well.