Best approach NetworkSrf or Loft or sweep2rail?

see file attached.
I have my profiles and my fore/aft lines linking them. They are all drawn from plans created before the days of PCs and as such one hopes the person drawing them had worked it out such that they all touch at their apparent junctions !
However zooming right in they dont. Its going to be difficult to make everything touch without analysing each and every missed junction. I then have to decide do I mess up the profile shape after all my careful plotting or the rail or a bit of both. Time dissalows further such work.

Should it be vital to have to do this, is there a way of getting such ‘misses’ indicated ?

Will such misses make a difference ?

NetworkSrf has tolerances so thats good.

I run NetworkSrf on default settings and it looks very good except it bulges out at the underside a bit at the front as indicated.
There are no controls to sort this.
I will have to split the curves and use sweep2rail, and I wish we had sweep 5 rail ! NetworkSrf is mentioned as to use if 3 rails or more are required but this bulge means NetworkSrf is not an option here.

As one can Loft open curves, when is Loft used and when is NetworkSrf used, and would such a choice be influenced by missing curves at my junctions ?

Is this suitable for Lofting. I select the top of each profile curve (the half U shapes) working in the direction of loft, selecting each in turn, command doesnt say about how to select the rails, so I start at the end of one and again progress my way to the last.

Hit enter and get a mess. No options to sort it out or are there ? I dont see normal or tight or anything. I see Developable. It also takes ages before hitting ok sees the palette disappear so this doesnt feel healthy ! Result to big to upload here so I was right !

So now what…Sweep2rail and do it in bits ?

BestFitLoft.3dm (272.7 KB)

NetworkSrf is making that bulge because it doesn’t have enough information in that area to do otherwise - notice how your longitudinal curves have a big gap there - so you need to add that information yourself. I added 2 curves - in red - and included them in the input for Network. The nice thing is if you use History, you can adjust the new curves to your liking and see the surface update.

This was just a two minute try, obviously one can do this more slowly and carefully, but you get the idea.


BestFitLoft-XtraCrvs.3dm (327.8 KB)

After I posted this I twigged the lack of profiles, but have then been struggling to take the last straight one and use it further along, OrientToCrv flipping it about, so yet another post.


I am desperate to know as it is exactly what I need ! I could make great use of that method.

2 mins, I have been struggling 1 hr !


  1. In Top view, select your 5 horizontal curves, call the CutPlane command and draw two “vertical” lines in the area of the gap. That command will create planes parallel to Right CPlane that intersect your curves.
  2. Intersect the planes with the curves to create points. Delete the planes.
  3. Use InterpolateCurve and interpolate through each set of 5 points to create 2 “starter” curves. Delete the points.
  4. Point edit the new curves to adjust their shape visually to something that corresponds to what you want. I added an additional control point on the “lower” section of the curve to give me more adjustability there.
  5. With History recording on, NetworkSrf all the curves, adjust your tolerances if necessary.
  6. Continue point editing the curves and see the surface update until you’re satisfied with the result.


Hi Mitch,
I have followed your instructions (now I am aware of CutPlane, I used to create mine using rectangle etc)
I get as far as 3 and draw through 5 points, the bottom of the shape bows right out.
I choose InsertControlPoint, select the billowing curve and click where I need a control point to get it back on the straight, and the curve I have takes on two straight lines with a small radius bend between.

Failed there, cant get the hang of adding that control point, each time the curve does that.

see jpg


Mitch, Steve, just FYI, Section works on curves and returns the intersection points.


Thanks, I always forget that… --M

I actually use InsertKnot and not InsertControlPoint, but that shouldn’t really matter - but you want to not click on one of the control points, but the curve itself. But it looks more like you used InsertKink and not insertControlPoint… What degree is your original interpolated curve?


Hi Mitch, Steve- The shape always changes with InsertControlPoint, whereas InsertKnot does not change the shape at all. Also, InsertControlPoint always returns a uniform result, regardless of the input. InsertControlPoint results are usually better behaved if you want to point edit after, which is generally needed.