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Intersecting solids cause "trim was unterminated" "didn't converge" (by Shrikumar.H)
After a couple of years using solvespace in 2D very happily, today I ran into an issue in my very first 3D solids project in solvespace.

Attached is a simplified repro of the problem. There is a rectangular solid (extruded) from which I would like to subtract half of a donut shaped washer (lathed). Later I will will subtract the other half of the donut as well using a second extruded rectangle.

The end result I want is -- in cartoon terms -- a washer-shaped hole burned on top of the slab of butter like someone placed a red hot donut on it, in a manner of speaking.

When I set the toroid to difference from the extrusion, the toroid lathing disappears when it touches the slab. Instead, I'd have expected a half-toroid washer shaped hole appear in the slab.

When I set the toroid to union, just as an experiment, the bottom half of the toroid disappears in a flash of red the moment it touches the rectangle. (Hmm, is solvespace reading my mind about my cartoon analogy :-)

And stderr contains a flurry of error looking like this : (small excerpt)

failed to assemble polygon to trim nurbs surface in uv space
didn't converge
have -31.437 20.799 0.000
want -31.439 20.800 0.000
distance = 0.00160566
didn't converge
have -31.437 20.799 0.000
want -31.439 20.800 0.000
distance = 0.00160566
trim was empty
didn't converge

It is quite likely I am doing something wrong, or have misunderstood something about extrude/lathe and differences.

This is a simple operation, I couldn't possibly have stumbled on a bug, can I?

-- //Shrikumar
Tue Mar 3 2020, 02:03:39, download attachment red-burning-donut-on-butter.slvs
(no subject) (by Andrew)
You have run into a known problem with the nurbs engine, for which the workaround is to 'force NURBS to triangle mesh'.

Also, to get the effect that you want, you have to create the toroid after you create the cubs. as what you have is a cube cutting a toroid, as the group that you select difference on cuts the rest of the model.

Hope this helps.
Tue Mar 3 2020, 05:46:47
(no subject) (by Shrikumar.H)
Super. Thanks for the quick reply.

I see. I did play with the "force NURBS" option, and I could see it made a difference. (thanks for confirming that's a known issue)

But I guess I did not try making the butter first to burn holes in.

Will try it.

-- //Shrikumar

PS: BTW when the lathing fails for some reason (like self intersecting solid), then it is not clear to understand in the user interface that it has failed.

You know, like when redundant constraints fail, you get blood red mayhem all over the screen. That blood bath is so primal, very hard to miss.

But when lathing fails, its very muted, very understated. For the first hour of my experiments with lathing I could not even be sure lathing was working or not working, and why the result didn't look solid like the tutorials and you-tube videos. Kept trying to enable/disable solid/outline/etc rendering in the view till my mouse finger wore out.

Perhaps some indication should appear screaming that lathing failed. And maybe point at the reason why (again, like redundant constrains shines a flashlight from the heavens, that's very helpful).

PPS: Thanks for solvespace! Its wonderful!!
Wed Mar 4 2020, 20:43:09
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