Disconnected lines -- close but not quite

[John_H555]

Fairly often I zoom in on a junction of lines, maybe three lines at the corner of a structure -- and find that one of them is not snapped to the intersection or ends of the others.

Is there a way to force a junction, or snap?  Or must the whole line be redrawn, snap to snap?

Thank you for your insights on this.

[Will J]

Hey,

I think I know what you're talking about. What I tend to do when I have a curve that needs to touch another, I do one of two things:

1. I draw a new curve using the unjoined one as a template, using near snap to snap it to both the lines.

2. I go into Control Point mode and hit transform > move and using end snap I snap the start point to the unjoined jine and then near or intersection snap to snap the point onto the other curve.

Does that help? A picture would help me see precisely what you mean .

[John_H555]

Hello Will,

Your procedure looks like it would help, I will follow it step by step and report.

Here is an example.  This a pylon type wing mount for an early Free Flight model aircraft.  I also include a shot of the underlying wireframe. If you look at along the red line at the bottom of the wireframe, you will see the uprights are disconnected. 

I have been using Network of Curves to get the surface -- it seems to ignore these flaws.  But the surface has imperfections, and I suspect this may be the root cause.

Thank you for your insights.

[Will J]

Yeh my method should work there, I model alot of ships and I get tat alot. Your curves have to be super neat before you can get anything good out of them . What I find work best is to use curves you've already drawn to draw new ones. For example if you have several profiles and want to make sweep curves, just use an interpcrv and use end snaps t get it right. Rhino has these little quirks, but the better you get the more you admit thats it's all your fault !

[gery]

I don't know how to do it with lines, but when 2 surfaces won't join and I can't see the problem, I just lower the tolerance value and they magically join, maybe there's something similar with curves

[Will J]

That could work, but lowering the tolerance should be a last resort. You should never do it if you want to RP or CNC the model, but if you just want to render it's ok . Hope you find the solution your after.

[Ivan]

I must say I really don't understand what your problem is.
If you are trying to make a surface out of curves, then first edit your curves so they touch each other.
It might seem a stupid question, but have you made your curves with Osnap?

Maybe a 3dm file would be helpful for us to find a solution...

[John_H555]

Here is another example of a gap in the same file, the pylon wing mount shown in a post above.

Yes, I use snaps.

It could be I produced these gaps because I was using elevator mode, as discussed in another thread. But however they got in, here they are. 

Edit the curves so that they touch each other, yes.  How would you do that, exactly, working in 3-space? 

I have played around with the idea of using the curve to establish a plane, and then declaring that plane to be the CP, but without a lot of success.   

[Ivan]

I would really like to have a 3dm file of this. I know it is stupid, but since I really don't know how experienced in Rhino you are, I must ask you if you used Near Osnap option. Or any other

[John_H555]

Hello Ivan -- the 3Dm is on its way to you by email. Thanks for looking at it, and for your help.

[Ivan]

ok. first, let me know if this is what you were after, then if it is I will explain how I got that...

[John_H555]

Wow! Thanks! Cleaned up very nicely, everything tightly joined. 

How did you do this?  I notice the new points spaced along the curves.

When I analyze the surface, as in this screen capture, it is much better too.

[Ivan]

yeah, I checked it with zebra and it was ok, but it can be smoothed out even more by reducing the control points count in my 3 curves and tweaking the curvature of these curves.

First, I'll try to explain what the problem was: Your outer curves were fine, all snapped to each others ends, but out of your three curves only one (and only one end of it) was snapped to a curve. That was why I asked you if you tried using Near Osnap option. It would snap anywhere along any curve.
So, first you should have used that Near, but the problem would occur when you would move control points around where the middle "horizontal" line is.

So I simply created Points on your curve, but I made starting, ending and Point on the middle curve snapped on three horizontal curves - for that I used Near. Then I simply created InterpCrv (if you use Curve with interpolated control points, you get to set the control points through which the curve WILL go through) using that Points (I used Point Osnap option so my cursor snaps to Points) That was it.

To be more accurate: I first created from front viewport three vertical lines which I extruded and then Intersected with horizontal three lines, just to get three points of one curve (starting,ending and middle). You could of course have created those Points with simply Projecting the lines onto three horizontal curves. That would give you the same result (even faster).

[John_H555]

Not quite getting this.

The idea seems to be to create a new curve, as Will J suggested above, using the old curve as a template.  This new curve has two new endpoints.  One upper endpoint is initially set as a Point on the upper horizontal line.  The lower endpoint is initially set as a Point on the lower horizontal line.  The new curve must also pass through a third point, which is initially set as Point on the horizontal belt line.  Once these three points are set, the new curve can then be traced from endpoint to endpoint over the original curve using InterpCrv, with the Near and Point snaps turned on.

It is not clear to me how the three initial points were set.  If you let the old curve define a plane, and then extend that plane, it will intersect the horizontal lines at the desired points.  I can see that.

I don’t see how to make it happen, however.   
 
“I first created from Front viewport three vertical lines which I extruded and then Intersected with horizontal three lines, just to get three points of one curve (starting,ending and middle).”

Did you mean, possibly, the Right viewport?  Is there a way to illustrate this process, maybe with a screen grab?

I attach a labeled version of the drawing.  Sometimes it helps to name the parts.  Let’s say here, for example, we are talking about re-drawing curve F1.

Thank you again for your insights. This is very helpful.

[Ivan]

yeah, I thought I'd confuse you with all the babling. Yes, it was the Right view I was talking about. I've just recorded you step by step how I did it, hope it will help you.

http://www.rhino3dhelp.com/video/curve-control-help-in-forums/