Having trouble lofting - can anyone help?


#1

I’m having bother lofting a shape. The end result is to be a canoe hull. The curves in my file are based on the cross sections of a canoe. From these cross sections I am trying to loft the canoe hull shape but something odd happens between the last and second last curves at the end of the canoe. I have a feeling it is because the last curve is perpendicular to the previous one - if this is the problem - how would I deal with it?

Thanks in advance of any advice


(David Cockey) #2

Can you post the file with the curves here?


#3

Tried sweeping? I usually prefer this in double curved surfaces. But if you like lofting then be sure to click on same ends on the curves


#4

Rhino Question.3dm (102.8 KB)

Sorry - couldn’t find the upload file option to begin with. I did consider sweep2 but came up with some odd results. Part of my problem is not knowing the idiosyncrasies of this particular feature of Rhino I’m sure and I consider myself reasonably experienced with the application. If anyone could have a look at the uploaded curves I would greatly appreciate it.


(David Cockey) #5

The file you uploaded only has the surface, no curves. Upload a file with the curves if possible.


#6

Hi David,

The surface is there but so are th curves that generated it. If you select and delete the surface you’ll see them.


(David Cockey) #7

First problem - try putting a curve through the bottom ends of the stem curve and the sections curves which is also tangent to the stem curve, It will have some reverse curvature. And if you don’t require it to be tangent to the stem curve there will be a kink - same as the edge of your lofted surface.


(David Cockey) #8

Here is a quick surface. Rhino Question DC01.3dm (150.7 KB)

I trimmed the stem curve so to make it closer to tangent with a curve along the bottom edge. Added longitudinal curves along the bottom/keel, top/sheer, and two intermediate curves. The intermediate curves help control the shape of the surface. Created a surface using NetworkSrf, then used Rebuild to simplify it to something reasonable and smooth the surface. Your input curves are very noisy and should be smoothed/faired before building a surface with them. They also can be considerably simpler - 10 or so control points should be sufficient for each.

There are other methods to build a surface from a set of curves like this but the method above is one of the simplest which will result in a reasonable surface.


#9

Your curves are way to complicated. They have 60+ control points. Simpler is better and then use option loose in lofting


#10

Here is a test for you - You can tweak the curves some more to get a more curved look if you want

Rhino answer roy berntsen.3dm (163.9 KB)



#11

Here is a more curved version using 4 control points
Rhino answer roy berntsen 02.3dm (158.7 KB)


#12

Hi Roy,

Thanks for your input it is appreciated. My Rhino tells me this file was created with an newer version but my update checker tells me mine is up-to-date. Are you using a WIP?

It’s actually a very specific region in the surface highlighted by a ‘dot’ when you open the file that is causing my headache. I can get a generally good quality surface despite the complex curves - I just rebuild it anyway when lofting to reduce the complexity. The loft I have so far is good because it’s very close to the curves which represent physical cross sections I lay wood strips along. My end goal is to get rid of the funny ‘kink’ in the surface between the first and second curve.

Could you have a look again if you have the time?


#13

WIP yes - V5 file attached
V5Rhino answer roy berntsen.3dm (157.9 KB)


#14

Here I used your curves - rebuilding to 9 controlpoints with a deviation at about 1.

NORMAL LOFT


LOOSE LOFT


#15

Now I can see - The problem is the front curve - Need to look at it some more


#16

It looks as you are trying to “force” a surface that is not smooth. If these are the actual sections the problem might bee that they dont have a nice curvature flow

Here are your curves

Here i sweept from rear to front


(David Cockey) #17

That’s what I was talking about in an earlier post.