Why does this happen when lofting curves?

[bishop00s]

Lofting curves... I'm running into an annoying little behavior, and I can't figure out WHY Maya is doing it.

When I loft a bunch of curves, I'm always getting this 'dip' in the geometry when you loft it right before the last one. I attached a picture. Essentially what I want here is a cylinder with a flat end... or relatively flat at least. I want the roundedness of the cubic lofting for the corner.... but I get this stinkin dip on the end even though those last 3 curves are all on the same point on the x axis.

Image:
http://bobspryn.com/loft.jpg

Example Scene:
http://bobspryn.com/cylindertest.zip

Thanks ahead of time.

~Robert

[failure]

When you build degree 3 loft maya does a cubic interpolation between curves, which has it's specific behavior, like it or not.

To have more control use more curves for loft, move curves to right places, or make a couple of separate lofts and then attach with positional continuity.
You can also use cylinder primitive and cap it with planar surface. Then make circular fillet for rounded corner.

[bishop00s]

To "attach with positional continuity" do I use the attach surfaces command and use the blend option? Or is there a different method you are talking about?

~Robert

[bishop00s]

I wish I understood more on how it is calculating the tangent of the surface between the 2 curves on the corner. It doesn't work the same as the cubic calculation on a normal 3 degree CV curve.

The surface tangent seems to always go a little bit beyond the axis... as in.. instead of just making a nice smooth tangent to the curve... like this:

it goes out of the grid and comes back in:

Understand what I mean? I can't seem to prevent this fully no matter how many curves I use.

The problem is I'm not just creating a cylinder... that was just an easy example. I have a lot more complicated curve that I have tediously formed a nice shape out of.

[failure]

Maybe try with revolve if it's suitable.

Regarding analogy vith curves:
It it the same calculation as for curves. But we are not dealing with CVs here. We are dealing with EPs since EPs are points thru which curve( or surface in case of loft ) is inerpolated.
And it's a bit tricky claculation that maya needs to do because EPs don't define the curve fully, they are just a result of the curve equation. Inerpolation takes kinda reverse engineering work and some guessing on maya's behalf.

Now, if you want to see the equivalent behavior on curves you must manipulate the curve's EPs. Try it out.

Anyway, having larger number of curves gives you more control over loft's behavior and usually fixes the "problem".
Add more and more curves untill you can control it the way you want it.

I can't give you any more useful suggestions unless I see the actual object you are modeling.

[bishop00s]

I came up with a different solution that will work for now.

I ran into a problem with trying to use the circular fillet after capping the end of the model with a planar, which seemed to stem from it not being able to calculate the real tight bevel corners of my shape.

I've been able to manipulate the curves well for every other part of the shape... its just for some reason at the very end when I am shrinking them down to close it off with a fairly flat surface they just start acting wacky.

I'll play with EP points to try to understand a little more about how it works.

If you would like to play around with the file and see if you can get it, that would be great. I put the file here:

http://bobspryn.com/shaver.zip (maya 6 file)

I have already lofted the curves so you can see what it looks like, but you can just hide that layer or delete it and reloft (probably the better idea.)

I'm just trying to close off that open end with a very tight beveled edge, and then essentially a flat surface.

Thanks a ton for the help man,
Robert

[failure]

Unfortunatelly I'm on maya 5.
Try to upload *.ma file. It should be loadable into v5.

[bishop00s]

Ok. Same link... I changed it to .ma

http://bobspryn.com/shaver.zip

[bishop00s]

Do professionals always avoid having the extreme hard edges like you would see on a nurbs cube? It just seems that since almost nothing has an absolute sharp edge like that... Even hard edges have a 'tiny' bevel. But I could see situations in where like I have a sharp blade that it would probably be ok to use the hard edge.

Are those edges sort of frowned upon in professional work?

[failure]

You can get away with sharp edges if your model is going to be rendered relatively small. Texturing and stuff like dirtmap can also help. But If you are for extreme closeups and details then you generally want everything to have fillets.

I looked at your file. What you have done is definitey not the best way to model this shape. Shape is to complex to be done as one surface. Do it from number of separate pieces ( they not need to corespond to actual pieces the object is constructed form in real world )

[bishop00s]

hmmm.... ok I hear ya.

Though I haven't really been modeling long enough to see how to easily do that with separate pieces. Where do you think you would have divided it up?

I haven't studied good patch modeling (or sub divs) yet so that answer might come when we study that soon.

I actually didn't find this method too hard. It gave me a lot of control. The problems I ran into are what we've been dealing with, and making those two seams meld into one was kind of tough. Its decent now but not perfect if you get close up.

Anywho. Thanks a bunch!
~Bob

[failure]

Having a lot of loft curves gives you control but you can mess up easily and you'll end up with too many cv's to take care of. Consequence is that your surface doesn't have a nice flow and small nuber of spans.

I suggest that you ditch the loft approach and start building from curves that are on "structure_curves" layer. Add some more profile curves to form a nice cage, then cut all curves, rebuild them and use birails and boundaries to make patches.

Latter you can make freeform fillets between patches if needed and attach them into bigger surfaces.

If I catch some time later today I'll play a bit with your curves and upload the result.

[bishop00s]

I was having problems with the bi-rail tool and getting those seams to be nice and tight. Maybe I don't know enough about bi-rail yet. I'll see if I can give it another try.

That'd be cool if you find the time to mess with it. Thanks anyway if you don't.

~Bob

[failure]

Don't know if you already cheked out these:
http://www.animagraph.com.br/DeathBrain/Basic/curve_tutorial.htmhttp://www.animagraph.com.br/DeathBrain/Ba...ve\_tutorial.htm
http://www.animagraph.com.br/DeathBrain/Modeling/Steering_Wheel_Tutorial.htmhttp://www.animagraph.com.br/DeathBrain/Mo...el\_Tutorial.htm

[bishop00s]

Reference photos here:

http://www.bobspryn.com/gallery/view\_album...bumName=shaving

[failure]

Here is one possible approach. There are coments in file.
( I didn't bother to model actual piece, just something similar )

If something is not clear, go ahead and ask

[bishop00s]

Holy crap...

I seriously love that there are people out there kind enough to put that much effort into helping someone else learn. That's incredible of you.

Thanks a bunch man... I get the general idea now. I'm going to go through your steps in your file to see if I can reproduce it before I redo it on my own.

Peace!
Bob

[bishop00s]

Just one question so far...

What exactly is the Paramter Range of the curves? Does that adjust the number of spans? No I guess that wouldn't make sense. What am I setting when I say 0 to 1?

Is it important to keep Tangents or CV's when rebuilding? I clicked NumSpans because it looked like you kept those the same. I believe I got the exact same result, I just want to understand exactly what I did.

Thanks,
Bob

[bishop00s]

Quick question... when attaching the surfaces, which kind of attach do you use? Connect or Blend? It seams if I us blend it will pull away from the other surface a little. Or does that not matter so much since I'm filleting them anyway later?

[bishop00s]

Last question... why are your fillets nice and round? Did you play with the middle hull afterwards or is there a setting somewhere?