Rebuild command fails to observe sharp corners


I need to get a few reference shapes just to help align some meshes as trying to line things up with just texture is not easy.
I draw a line, project to surface of mesh, it now has many points.
I run rebuild command to simplify the line and get rid of the points, 28 seems a good start for points but a very lazy curve runs through the sharp bends. I am now as high as 60 yet still the sharp corners are not being followed .

What is best command to redraw this line, laying in a straightish line on the flat areas and observing bends ?

I may even use line through points to replace the long straight portion.

I need to get profiles from the mesh and thought my method project then rebuild as an initial stage of getting some reference shapes to align the meshes together would work.

rebuild fails to observe sharp corners.3dm (257.8 KB)

Correct, rebuild alsways makes a G2 curve.


I saw degree 3 and took false faith, G3 and degree 3 not same…oops.
So as said

What is best command to redraw this line, laying in a straightish line on the flat areas and observing bends ?



Hi -

Create a new polyline and use the projected curve as a visual guide.

Hi Steve - I would say do it in pieces and Join. I would not rely on anything automatic, I’d build my own lines for the straight bits and curves in between.
rebuild (PG).3dm (271.2 KB)


gosh I am quite surprised there isnt a command that rebuilds it to G3. sees straight parts and uses 2 or 3 points and a few more for a curve.

perhaps settings of straight enter number of control points,
curves, enter number of control points.
perhaps drag select a circle over bends to indicate areas for the curves option.

So it has to be hand crafted then, but with so many profiles, hundreds to do, that need de pointing thats a lot of work I thought an auto build would tackle.

Oh Dear.


Hello - if you rebuild to degree 4 or more, the curve will be G3 or more.

Hi Pascal,
ok set to 4, worked my way through , 87 does it, 88 loses it as does 86, going more doesnt see a closer match it varies per point number.

I like my idea of an option asking for selecting parts of the curve for the ‘curvy’ work and parts requiring straight. Perhaps get it to match for the corners then cut and rebuild the straight parts further.


Hi Steve - I am not sure what G3 has to do with what you are doing, but I’ll let you work that out.


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I thought you were saying here or suggesting, that I needed G3 for it to tackle sharp corners and to get G3 I had to enter degree 4 ?

Did I misunderstand ?

I will re-ask, What settings if any in rebuild will get this line with straight parts and sharp corners with a minimum of control points ?


Hi Steve - I never mentioned G3 apart from a response to your wish that you could get G3 curves from rebuild - you can buit that is neither here nor there for what you want to do. You can throw enough points at it in Rebuild to kind of work but I am not sure what the goal is - if the goal is to get a clean simple curve, again:

(Rebuild samples evenly spaced points on the input curve and interpolates; it does not pay any attention to needing more control points in areas of higher curvature and fewer on staigther bits - so if you give it enough points to stay close to the high curvature areas, you will way over populate the straighter parts - The more points, the more likely the curve will wobble locally back and forth -

the tool is not designed to just take any curve and make it nice. At some point you need to draw your own.)


you can also use RebuildCrvNonUniform with a very low tolerance of 0.0001 but you still need minimum 150 points which is 10 times less than your original.

your curve is very complex in changes and bumpiness, trying to simplify the original naturally will result in less complexity. also dont forget that you have a pure polyline here, converting that into a curve will also change its appearance.

you can use SimplifyCrv to get rid of a few extra points inbetween straight lines but that might not be enough for you.