Why do these Face Curves fail?

EvanReese

I sometimes see cases with opCreateCurvesOnFace where the 0 parameter or the 1 parameter fail and highlight red. In many cases it doesn't do this. What's going on with this? Here's my example:
https://cad.onshape.com/documents/48ff65c2b30601ca3bc3611b/w/70b5eaf200aacbabaa89a3b8/e/0b9bcf8bdaf6dc529ba2b769

 

Alex_Kempen

I'm not sure why some cases are failing while others do not, but if the 0 and 1 parameter curves always correspond to the top and bottom of the selected face (which must necessarily be defined by edges), couldn't you use opExtractWires on the corresponding top and bottom edges, and only use opCreateCurvesOnFace for the intermediate curves? This would also hypothetically allow you to make converting the top and bottom edges into curves optional, which might be desirable. The hardest part is probably querying for said top and bottom edges, but I think either qLoopEdges or qAdjacent should work for that in most scenarios.

EvanReese

Alex_Kempen said:

I'm not sure why some cases are failing while others do not, but if the 0 and 1 parameter curves always correspond to the top and bottom of the selected face (which must necessarily be defined by edges), couldn't you use opExtractWires on the corresponding top and bottom edges, and only use opCreateCurvesOnFace for the intermediate curves? This would also hypothetically allow you to make converting the top and bottom edges into curves optional, which might be desirable. The hardest part is probably querying for said top and bottom edges, but I think either qLoopEdges or qAdjacent should work for that in most scenarios.

Good suggestions, Alex. yes, I've considered some workarounds, and I'm sure you'd be able to come up with something good. I hope it doesn't come to that. I also don't like that it highlights red by default, which could confuse a user (I didn't add a debug).

I'm thinking it has something to do with how trimmed surfaces work in Onshape, even though this surface is straight out of a loft, perhaps the 0 and 1 barely fall off the end of the visible surface due to some tolerance thing with the software. Anyone know for sure, and whether there's a cure?

NeilCooke

I don’t know the answer but my immediate reaction (before reading Alex’s reply) was to do what Alex is suggesting. Probably a tolerance thing.