Loft surface from nurbs curve

[ben@gibson.co.nz]

I am having trouble lofting surfaces in 2023.

I will draw a nurbs curve and then use the loft tool.

rather than following the curve it will simplify it down to something very basic.

Below you can see 2 nubs curves and then the resulting lofted surface.

Is there a preference I don't know about? it was working fine for me in VW2022 

[Claes Lundstrom]

What are the settings on Shaded Options? Low? Have you tried something higher? 

[Pat Stanford]

If Claes idea does not help, can you copy and past the loft into a new file and see if it works ok there. If not, please post the file with the loft here so we can take a look.

[ben@gibson.co.nz]

Thanks Pat, I tried Claes's idea. I did have shade set to low but it made no difference when I changed it to high. The loft tool does not seem to work at all if I have more than 2 nurbs curves.

test.vwx

[Pat Stanford]

How did you convert your NURBS curves?

 

When I try with your curves I get the same circular loft.

 

When I make a similar shape to yours starting with a 2D polygon and then convert that to a NURBS  and loft those, then it works.

 

Your original curves loft is you draw a connection curve between the two curves and then loft using the 3rd mode of the loft tool, Birail Sweep.

 

I traced over your curve using the Besier mode of the 2D Polyline tool and ended up with a curve with 20 vertices. I then converted that to NURBS and it ended up as a second degree NURBS curve with 20 vertices. Duplicated and lofted in the first mode and it worked fine.

 

I converted your curves from 3rd degree to 2nd degree just by changing the number in the OIP from 3 to 2. They then lofted correctly.

 

When I converted my simplified  curves to 3rd degree I got the same circular loft you are getting.

 

I don't have time to figure out what the difference is between 2nd and 3rd degree curves and why that effects lofts right now, but I hope this helps you get what you need out of this.

 

Convert to 2nd Degree and move one.

[Katarina Ollikainen]

Hi, don't know why it doesn't follow the profiles, but if you add a rail, it will work nicely (I assume this is the result you're after?)

[ben@gibson.co.nz]

Thanks that is very helpful. The Nurbs curve was drawn with the NURBS curve tool.

Weird that I would need to draw it with a 2D polyline tool and then convert it to nurbs, but that is certainly a solution. Thank you 

[Benson Shaw]

@ben@gibson.co.nz

 

I get same cylindrical loft in your test.vwx file.  I wonder if problem is the file itself rather than those curves?

 

Anyway I tested several ways:

• Deleted all other objects. Moved curves to origin, etc -  No joy with Loft no Rail.
• New NURBS curves of similar shape, same location, or if moved close to drawing origin produce the same result in that file.

I did make a proper loft in that file by converting the NURBS to 3d Polys, then convert those to NURBS.

 

Best result, though . . . Copy/Paste in Place the two NURBS curves and into a new blank vwx file. They loft as expected.

 

Loft mystery!

 

-B

[AlanW]

Hi I there must be something wrong with they were originally drawn.

Convert to 3D polys and then back to Nurbs and works fine.

[Claes Lundstrom]

22 hours ago, AlanW said:

Hi I there must be something wrong with they were originally drawn.

Convert to 3D polys and then back to Nurbs and works fine.

 

 

I tried that and yes the shape is correct, sort of, but it's not a generic NURBS surface in the sense that it can be set to any mesh resolution.