R8 Section Curves - Poor results compared to R5

I routinely use Rhino to do various operations, including some retopology work on scanned meshes. I’ve noticed since v7 and now in v8, the quality of curves using Curve->CurveFromObjects->Section to extract cross sections has severely degraded - Forcing me to go back to v5.

The curves are neither clean, nor are they closed. Is there a setting or configuration I am missing? It seems to me that the curve quality and usability should be better in v8. I feel like I am getting “Less Than” using v8 vs v5 in this regard.

The curves output from this function in v8 are dirty, inaccurate, jagged - OPEN - and practically unusable.

One notable difference between the two is that the v8 one seems to go up and down in the Z plane, whereas the v5 one is truly planar without that undulation in the Z, like a wave - which is completely undesirable for a section created using Ortho and snapping to surface planes.

Can anyone help?

Hi BW1,

Can you provide an example and environment info? Thanks!

Help us help you

https://imgur.com/skZkFcU

https://imgur.com/elQ0RSZ

R5 Curve on left. R8 Curve on right.

The R5 curve is continuous and closed. Section curves in R5 are 99.9% always closed. R8 section curve is junk.

I don’t have any way to attach the Rhino file. Please post suggestions for doing that.

Neither one is exactly high quality as far as vectors go…but the R5 one can at the very least be used straight away for extrusions etc with minimal tweaking/rebuilding.

Hello- please attach a V5 Rhino file that shows the problem - you can so that via the upload button at the top of your message or with a drag and drop.
If the file is large or confidential, please send to tech@mcneel.com, with a link back to this topic in your comments.

-Pascal

R5CompareB.3dm (139.9 KB)

R5 Generated Curve (X Section of 3 flute tool) and R8 (latest release) Curve on their own layers attached.

Hello- I don’t see anything to section in the file - I don’t dispute the results may be different, however we need to be able to reproduce the problem in order to fix it, so I need whatever you sectioned.

-Pascal

Hold on…I have to severely decimate the STL…

R5Compare.3dm (1.4 MB)

Same file with HEAVILY decimated STL. It’s not going to be apples to apples because the original STL was 114MB, so keep that in mind…

Hello- change file tolerance to .0001 in V8 and have a try - any better?

-Pascal

A post was split to a new topic: Make2D in rhino 6 and seven simple don’t work

Hi Pascal,
Yes, that did seem to improve the result, but it is still a collection of open vectors, requiring a bit of editing to get it closed etc. Reducing the tolerance to 0.0001" seems to have greatly reduced the amount of Z undulation in the section.

I’m just wondering what changed between R5/6 and R7/8 with that tool - Maybe it could use a little “looking at” by developers to see what improvements can be made? (pretty please).

I use that function quite often in my workflow…and I find myself just going back to R5 because it just works so well…but then the agg of piping it over to R7/8 to do the rest of the work via QMesh/SubD is clunky…yanno?

Thank you for the help - You’ve always been very helpful!

Hello- I get a closed curve on the mesh you sent, at .0001 - if you do not, lets dig some more.
Mesh intersection has indeed changed over the years.

-Pascal

hi folks. I reported this back in December, still an issue for me as well…

(side note, updating my nvidia driver didn’t fix this)

I really miss my good ole’ section command please tune it!!