Thanks guys.

I've attached a screen capture of the section I am attempting to loft. I've now tried it full hull length right round the stern using both loose and normal. It is really close using either option. It would be a really smooth hull! Also, a one piece surface would make trimming and then extruding the "plates" a doddle. The networked version created extrusions with internal surfaces that I had to hunt down and delete.

>My guess is that I won't be able to actually do anything about this
>stuff but with some examples it can help me to at least get some
>gears turning to maybe be able to improve it in the future.

And that's one of the great things about this software. Even if there is no way to achieve this I am impressed that you give consideration to ideas from your user base. Doesn't happen much in the software world.

Hi Danny,

>Just had a quick look at this, if I may, the approach I would
>take would be to use a combination of Network and Blend
>ie. Network every second panel and use Construct>Blend
>between them to get tangency.

Hadn't even considered that as an option. I just tried it but couldn't get the blend to work (blend is one of those commands I struggle to understand). In the attached, should the selected curves blend or am I thinking about this all wrong? The second attachment shows what I got. I don't think I'm using blend correctly at all!

Hi Mark,

> I just tried it but couldn't get the blend to work...

To blend between two surfaces you have to pick the edges of the surfaces not the curve you generated them with, to do this, hide all your curves so you don't get confused between picking a curve and a surface edge, then pick the surface, mouse over the edge and pick again to select the edge, do the same with the surface you want to blend to and select Construct>Blend and a surface should be generated.
Play around with the options to see what affect they have.

If you need a mini tute let us know.

Cheers
~Danny~

Hi Danny,

I was on the right track. I didn't hide my curves and was selecting those instead of the surface edges. Must remember that for the future.

This method seems to have a different sort of limitation. The blend creates a gap as shown in attachment 1. This can be adjusted out somewhat but creates a curvature then at the bottom per attachment 2. Have I missed a setting?

My problem with the networked version is, I think, that the curves are traced from paper plans of varying quality which have been scanned, jpeged and coffee stained to within an inch of their lives. The accuracy of the resulting nurbs curves is questionable and any problems between the networked surfaces shows up at the joined edges. I have rebuilt my curves in the vertical which helps a lot. I did not try it in the horizontal. Perhaps I should have. If I rebuild all curves, will a hull as curvy smooth as the lofted version be the result? The problem in the horizontal that I can see is that if I rebuild the segments of the curve I get better but still wavy curve segments. If I join the segments and rebuild as an individual curve, the curve shape changes slightly, enough for the horizontal and vertical curves to no longer intersect. This would then require me to snap curve points.

Hi Mark I think I get it - if I understand correctly, you are doing a loose loft using these profiles:



But then the part that you want to nail down more is actually this side of it here:



Is that correct?

But basically Loft does not give you such specific control over the side edges like that, sweep or Network are the ones that give side edge control. But more pressure to constrain a shape tends to make for more compressed undulations in it as well which I'm sure you've run into a lot.


But do these pieces here have to be separate surfaces:



What about making a larger single Loft that includes those pieces all within it, that would help to make them touch properly. You can have a sharp corner in a loft profile, that's ok.

That would also involve making some of the rear sections be extended up somewhat extra, and then if need there to be a space in that area you would cut it out with a trim here:




- Michael

Hi Mark, attached is a 3DM file of the kind of thing I'm talking about - here you would do a Loft (Loft Style: Normal seems to match your top side curve good) with these taller profile pieces to make that upper part along with the lower part all in one Loft rather than as separate pieces.

It's ok to have a kink in the profiles, but it is also good in that case to make sure that each profile is made up of the same number of segments, so I split a couple of the back upper parts to make a segment arrangement that kind of continues those strips throughout the loft.

When you do a loft in one go like this with kinks in the profiles, the generated pieces will all be sure to touch each other.

So that would solve your problem of having gaps between pieces anyway...

- Michael

Hi Mark,

Had a better look at this Hull, and I'd like to correct my self in saying that this is more suited to lofting after the curves have been optimised like you said and some finishing off with some blends.
It was a nice exercise, some learning for all I think.

Cheers

That's the technique Michael! Works great. Why didn't I think of doing it that way?

This also works for that rudder area. I've extended the curves down and trimmed. With care I might be able to extend it right to the stern without need for any networking at all, for a one piece hull.

I've included a quick render and the result looks near perfect.

The key points I think are to extend and trim and to keep the same number of curve segments.

Thanks Michael and thanks Danny and Burr for your input.

That's great Mark, I'm glad that will work for you!

It tends to be a bit tricky to get that "build extended then trim" modeling instinct down, it just is a bit counter intuitive to think about building a part of something that you don't actually want at the end.

But it can greatly help to simplify the initial construction with a more regular topology so it tends to be a good habit to develop with NURBS modeling in particular.

Anytime you find yourself kind of sticking together smaller individual fragments and wishing they were all smooth to one another or behaving similar to being a single surface instead of separate pieces, that's a good warning sign that a "build extended then trim" approach could be worth considering.

- Michael

Michael has reminded me several times to try not to create the exact shapes you want all in one operation.

It's better to create a very close shape with unwanted areas and simply trim them away in a second operation.

Being that ship hulls and spaceship hulls are similar to a degree, I've learned a lot from this thread also! ;-)


-Will

From the Michael file
Something I don't understand : seems number of points are not accord to the sides?

Hi Pilou,

> Something I don't understand : seems number of
> points are not accord to the sides?

Are you just looking at the control points of the curves?

Some of those curves just happen to be drawn with a different number of control points in them.

There is no restriction for surfacing commands like Loft, Sweep, or Network that each profile curve needs to have the exact same number of control points in it. It is allowed to use curves that have completely different numbers of points in them.

MoI goes through some steps to automatically synchronize curves like that up to one another when constructing the surface.

- Michael

Hi Michael,

Unfortunately I've hit another snag.

The hull looks great until I try to do the very stern. At the stern the bottom points need to be on the hull's centre line. In the first attachment I have left the curves rounded (no corner point). The hull lofts the way I want it to. In the second attachment I have added a corner point and snapped it to the centre line. Attachment 3 shows the problems that result from doing that.

I am at a loss. I can't see any way to get the stern capped without having the rest of the hull come to the centre at some stage. I can't do that without a corner point snapped to the centre. I have tried this many different ways and have rather lost track of things now. What to do?

Hi Mark, can you post a 3DM file with your new curve setup in it that you are having problems with?

That would make it easier for me to check it out and possibly recommend a strategy.


So I know I just got done telling you lofting things in a larger sheet (and then trimming them), but if you have a piece that behaves more like a protrusion from a base shape, then that may not fit into that same category. It will probably be something like model the protrusion as a different pieces and either fillet or blend it in to the other piece.


The "build in one large piece" type strategy is for things that are more like one smoother sheet. It can change shape to a certain degree over it, but trying to pull out a thin protrusion is too much shape mutation, such things will likely need to be a separate piece for the protrusion.

- Michael

Hi Mark, so what I'm talking about is right about in this area:



Right about there begins a significant mutation in the shape.

That then becomes a situation where you are actually trying to loft too much at once rather than not enough at once... I know it's tricky to find the right balance.

When you try to make a protrusion like that all in one go it will be very difficult to avoid awkward shaping.



Basically what happens is that MoI tries to match the whole length of each profile evenly with the next one.

It's not smart enough to figure out all on its own that different regions of your profiles should be matched with only some individual portions stretching out.


To try and describe that a bit better, in your situation there it looks like you want these portions to be mapped more closely to one another:




But then have these parts at the bottom kind of stretch out separately from the above parts:




Loft does not understand these kinds of sub-region matching automatically. You can help it by splitting the profiles into segments so that the segments will control the matching but when you have such a major shift in shaping that more calls out for a separate piece there and attach it to the main one by fillet or blend.

- Michael

Mark,

Warship hulls using NURBS is both my nemesis and sweet spot. I do not have time right now to go into any detail (but will soon) about how to help you.

I think that you are making things very hard for yourself by having too many curves (stations that is), that are irregular and with many points. Also, as said before (I zoomed past the thread), it might be counterproductive to generate the entire hull in one go.

British cruiser hulls nearly always display a knuckle at the bow. This you can add later and therefore disregard the part above the knuckle for the hull generation proper.

In my experience, it is better to work with longitudinal curves (waterlines) than with vertical sections (stations) and to use only as few as absolutely needed to generate the shape you want. Using curves with the absolute minimum number of control points also pays handsomely. 5 points are all it takes to control a simple curve, generally: begin, end, largest deviation from straight line and one point either side of it to control the curvature.

The stern is a more difficult area, but one that can be tackled rather painlessly using a combination of network curves, lofts, blends and sweeps depending on the case.

I will get back to this when I have time to work out an example.

Hi Michael,

Many thanks for your continued efforts with this. I've decided to go with my networked hull for this model. It has a hollow which I didn't notice before which is bothering me now but much additional work has been done on it (plate extrusions etc) which I've decided I don't have time to redo.

This has been a very worthwhile exercise with some water still to flow under the bridge (ship?). I have another one to do which I will attempt with a loft and trim mindset from the beginning.

Jean-Paul, I eagerly await your thoughts on this. I have already referred to several of your threads for ideas.

>In my experience, it is better to work with longitudinal curves
>(waterlines) than with vertical sections (stations) and to use
>only as few as absolutely needed to generate the shape you
>want.

Unfortunately, longitudinal curves are almost never given in the plans I have so I have had to work from stations.

I couldn't resist attaching latest progress render and a two minute scene render (with some odd coloured water!).

Cheers

Hi Mark, well your current renders there are looking great!

- Michael

I wanted to fool around with this a bit. I talked to a guy who told me that using the waterlines as opposed to the stations is how they build hulls. The stations are more a way to get your waterlines. So I took your loose loft of the stations that created your shape fairly close to what you want, then I created a direction array of a few lines out to the side and projected them onto the side of the loft. Then I ran rebuild curve on those new waterlines and used about 20 points to get curves with no deviation. I then lofted with "normal" the waterlines and got a good points structure that could be manipulated a bit easier to adjust areas. I could do this while the loft was still active in history and just use the points from the input curves.

I think I could go back to Station manipulation by reversing the process, but it is much harder to manipulate the overall shape by stations.




Any further input from you Mark, and JP is appreciated.

Hi Burr,

Wow, that looks great. Thanks so much for following this through. I wonder if that is the technique that Jean-Paul uses?

I need to have a go at this today. I think I understand the technique and will get back to you with results. I really hope I can duplicate what you have done there as this is looking like the method for hull generation.

What a great forum this is. Thanks again Burr :)

Mark