Modeling to Cross Sections

[Milton Shupe]

I would like to start a discussion on cross section modeling with the objectives as stated below:

1) Identify best methods of modeling using cross sections;
2) Improve on the processes to expedite this basic and fundamental task of getting the fuselage shaped perfectly.

My method, which is crude but effective, is to simply:

1) create a planar, map it and apply the cross section drawing (I use Fit to Bmp to avoid stretching-then I scale it to proper size), then
2) clone the original planar mapped for each cross section and name per the cross section position;
3) position each planar at the appropriate longitudinal position on the side view aligning the drawing properly on the cross hairs center-line and vertically;
4) create a 18-24 sided cylinder, deleting all but the front poly then change its properties to "See through";
5) clone and position each poly just in front of its respective cross section naming each by the cross section letter.

Now I have all the cross section polys ready to shape to the drawing.

6) Once all are reshaped, I delete all the cross section poly faces leaving only the vertices.
7) Then I begin connecting the cross sections but hand building polys from cross section to cross section.

This is a cumbersome process (takes 1-2 hours for each phase) but gets all the cross sections and fuselage shape done perfectly IMO.

Let's discuss alternative ways to do this and maybe help those of us who model, or would like to start modeling, become more productive and effective at what we do.

I attach an example 1/48 scale drawing cross section view of the Fiat G55. I have larger versions of the full set if anyone is interested.

 

[Milton Shupe]

Attached are screen shots of various stages in the process. EDIT: This is an example of my start on the CANT Z1007.

Applying the 3-view using "Fit to Bmp"
Completing the cross section planars
Shaping a poly to the cross section
Finished base fuselage

Creating/cloning all the planars and positioning them is fast, just a few minutes.

It takes maybe an hour to adjust vertices to fit the planars.

It takes maybe an hour then to construct the polys to connect the cross sections.

 

[Ivan]

Hi Milton,

I can't quite see how the finished base fuselage resembles a Fiat G55.
Is that the right model?

Thanks.
- Ivan.

 

[Milton Shupe]

Hi Milton,

I can't quite see how the finished base fuselage resembles a Fiat G55.
Is that the right model?

Thanks.
- Ivan.

LOL No. The Z1007 is the most recent example of what I have done here so I used the gmax screens for graphics examples.

The G55 simply had a good cross section set that I used to introduce the thread.

 

[Allen]

I use a 16-12 sided cylinder (CFS2 builder) with a load of Height Segments.

Convert the cylinder to a Editable Mesh and Use Vertex mode with Select and Uniform Scale and Select and Non Uniform Scale to shape the first segment. (I work nose to tail and root to tip). Than I select all of the other segments Vertex mode and move down to the next segment to shape.

 

[Ivan]

A VERY Similar Model

Hi Milton,

Here is a VERY similar model I built a while back. (Still stuck in my paint shop.)

While it isn't sposta be a Fiat G55, with a proper paint job, I don't think most folks would be able to tell the difference without some measurements of exact dimensions. It is amazing how similar the Italian fighters looked to each other.

- Ivan.

 

[Milton Shupe]

Yes, I agree; they are very similar.

 

[hairyspin]

Splines, CrossSection and Surface modelling

I read about this years ago on Netwings: it's only really good when you have very high quality drawings or information, but I like to get the best 3-views and detail drawings I can for a model...

Like Milton says, line up your drawings using the drawing's reference centre and the Gmax home grid:-

Drawing splines to trace over the curves of the drawing can be tricky: the spline isn't always easy to see, so here's a helpful Gmax feature:–

I also use the home grid to set even spacings for the vertices making up these splines. With the cross-sections aligned and a new spline for each duly traced, you get a lovely collection of curves:-

 

[hairyspin]

The data for this aircraft also gives the distance aft of the nose for each fuselage cross-section, but first I want to have all the splines' pivots on 0,0,0 and aligned to the Gmax world, so select Affect Pivot Only:-

With the pivots all correctly positioned and aligned I can now use the coordinates supplied with the aircraft data to position them.

Now for the magical bit:–

 

[hairyspin]

Modifier Magic

Click on each cross-section spline in turn. If you select them out of order you'll finish up with a contorted, folded result:–

As you Attach each spline to the first one it will change to the same colour. Next add a CrossSection modifier and finally a Surface modifier: this is where many say urgh! and give up:–

And the final result:–

There's some tidying up to do, especially around the cockpit where the fuselage steps sharply down to make way for the canopy. This mesh is however ready for conversion to e-poly, cloning and mirroring.

Problems with this method arise when you have different numbers of vertices from cross-section to cross-section, which is why I use the home grid as a guide. This method is also fabulous for wings when you have good info on the aerofoil being used.

 

[Milton Shupe]

Thank you Tom; perfecto! I was hoping that you would post this.

"I also use the home grid to set even spacings for the vertices making up these splines."

This is a great idea; it's the part I always have trouble with.

 

[hairyspin]

Cleaned up, clone and mirror, weld centre vertices and boolean cockpit cutout done.

 

[Milton Shupe]

We need to stick this one.

 

[Milton Shupe]

Tom,

Would it be possible to redo these posts as you did originally. Seems all the screen shots disappeared.

I wanted to use this technique for my new project.

 

[hairyspin]

Pictures are back, I got a new hosting service. I'll start restoring others now as opportunity presents.

 

[bdf369]

Pictures are back, I got a new hosting service. I'll start restoring others now as opportunity presents.

Could the missing images in this post be restored? Much appreciated.
http://www.sim-outhouse.com/sohforu...max)-Tutorials&p=805203&viewfull=1#post805203

 

[Firebar]

If I can add something to what hairyspin said as a method:

If you can draw your fuselage with a set of cross sections with limited vertices, and the same number of vertices in each section this works best. You can use the "Surface" modifier's iteration command together with the "divide" tool to give your fuselage the required number of sides (This works quite nicely for aerofoils too).

You do this be going to the segment sublevel of your attached sections, while you're there select all segments, then use the "divide" tool to give the required number of sides. When you apply the surface modifier now you can use the steps set to 0 to have it exactly as you drew, and then use the threshold option as low as possible so it doesn't merge any close vertices.

The only caveat that I've found is that after you hit "Divide" you may need to go to "vertex" sublevel and change all of the vertices to be corners or it might do funny things.

 

[Sundog]

This is quite interesting. My method tends to be more tedious, but it's what I know. I usually lay everything out in AutoCAD; meaning cross sections and basic profiles, then import that structure into 3DS Max to mesh. I usually set the cross sections up on a radial grid so that all my longitudinal lines run parallel down the length of the fuselage or across the wing.

Now that I'm going to start modeling again, I should try some of the methods you guys use to speed up the process. But I'm also going to have to learn new software, as my 3DS Max is old now and the new version is lease only (No thank you). I might have to learn Blender. There's also a lofting method I've been meaning to try;CAD Lofting Method.

Some of my earlier work is attached for reference to my method ; He-219 work for T4T shown in the next reply.

 

[Sundog]

Found the He-219 model; This was optimized for a relatively low poly for a Multiplayer game; I also show how I make models like this as mentioned above.

 

[hairyspin]

Once you have the geometry to your liking, apply a Reset XForm (it's on the Tools tab in Gmax and 3ds Max) before any mapping or animation. This way the program has an accurate handle on the object(s) you've just built.

This issue just came up elsewhere giving the modeller a heap of extra work to do!