Proper Workflow for Seats?

[JSantocono]

Hi dfunk,

It seems as though that if I start with either a box or a plane that at some point the 4 corners become an issue when trying to create a perfectly rounded seat back and seat bottom (top and bottom boundries). I can eye-ball things fairly well, but seem to always end up with some dimples where these corners end up residing. What's the best approach to start with???

Well, I probably would aproach it like you did.....starting with a primitive plane and polygonal manipulating. I can help you with the dimples if you send me the file.

Second question is this:
When I try to "thicken" a complex form such as this seat, the perpendicular edge that's created seems to deform as it flows along the edge of the model. How do I perform thicken without the edge going bananas?

Depends on the case.......but a probable solution is to tsThicken before doing the tsCrease.
The model can help me here too to give you a solution.

Or how about this one that's a little more geometric but still could benefit from an organic modeling tool for the seat back? Same process???

I think that the first example (more organic) is perfect for T-Splines. Totally doable.
The second example (more geometric) can be done in T-Splines but is not the best model to make with T-Splines, at least not completlly. Maybe only for the backseat. You can approach it on the same way.

Anyway, I can help you with a solution with the file that have the problem.
JuanS

[JSantocono]

Hi dfunk,
Sorry, but I dont see any dimple here. I see a vey smooth surface. Maybe I have been working with too many models today sorry if I miss it.
Can you point them out?

Thanks,
JuanS

[Nicholas North]

I took a quick look at the posted model, and it appears that one of the reasons that the star points aren't looking as smooth as they could is that the model doesn't have very uniform knots. The shape will change somewhat, but have you tried using the tsMakeUniform command on this model?

Another thing that you can do is adjust the star smoothness in the T-Spline options (tsOptions). This helps a bit, but the uneven knots is probably the big culprit here.

-- Nick

[Adam Helps]

I'm glad that it works for you .

Be aware that a star smoothness of 10 is very high. Increasing star smoothness means it will use more and more surface curves to define the surface around star points. Each time it increases, it cuts the existing curves in half. For a star smoothness of 10, the curves around the star point in the final NURBS surface will have a spacing of about one-thousandth of the original face. Check your NURBS output (tsConvertToRhinoSrf, Explode), and make sure you're happy with it.

You may be able to get a satisfactory result with a lower star smoothness. We rarely need it any higher than 3 or 4. But if you need it, there's nothing wrong with the higher smoothness--it's just good to be aware of the consequences .

As for your other question, it's quite difficult to get a corner to form a smooth edge like you're asking. We usually extrude all the border edges and allow some star points on the interior. However, that's not the only way--it is possible to carefully choose control point positions to give you a smooth edge. You can get G1 continuity just by making the tangency handles and the corner point collinear, but to get it any better takes some difficult calculating. We've debated how one might create tools to make it easier, since computers do math pretty well, but I don't think we have a favorite answer yet.

[Nicholas North]

As Adam suggested, one good way to deal with these corner points is the following:

1. Turn off symmetry with tsSymmetryOff (we'll be working on the whole surface)
2. Pre-select the edges on all four sides (turn the HUD on first, Ctrl-Space)
3. Run tsExtrude to add a smooth layer of faces around the outside edge

Here's the model after performing these steps.

seat.3dm

TSplines_Test 004 with extruded border edges.

(733.17 KiB) Downloaded 89 times

Also, one good way to manage high star smoothness is to keep it as low as you can until you need it high. For example, if you bump up the star smoothness right before you convert to a Rhino polysurface then the star smoothness gets "baked" into the result. Just be aware that you'll have quite a few isoparms around stars.

Hope that helps,
-- Nick

[JSantocono]

What I was getting at earlier is that if I start with a rectangular plane and want the top and bottom edges to end up as full rounds, I'm still confronted with the 4 corners of the plane. These vertex points act like knots, not control points... so it's difficult to get a nice smooth edge. How do I address this???

You can select the corner control points (the "knots") and delete them..... (I usually delete what I dont want)

JuanS

[modern]

TRY