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Date Topics  
7/09 Creating stunning jewelry designs with T-Splines View
5/07 How to approach modeling with T-Splines View
3/07 Carl Bass reintroduces T-Splines for Rhino View
6/21 Transitioning from NURBS to T-Splines View
12/07 Footwear modeling with T-Splines 3.3 for Rhino View
11/29 New T-Splines reverse engineering tools View
10/28 How T-Splines changed my aproach to making jewelry in CAD View
09/29 Modeling a water gun View
09/07 Car modeling:
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07/06 tsElements intro
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06/22 Free-form Architecture View
06/15 TS Pipe command View
06/08 T-Splines for Rhino intro View

T Splines Stars and five sided polygons

A support and feedback forum for Autodesk T-Splines Plug-in for Rhino users.

T Splines Stars and five sided polygons

Postby Proterio » Tue May 24, 2016 9:26 am

Hello all :)

Been working with TSplines for a while now. Watched a LOT of videos!

I am still not clear about what happens within TSplines when you end up with a star (the intersection point of five lines) and polygons that do not have four sides ie triangles and 5 sided "squares".

In the 3 part webinar by Kyle on modeling a car body I heard mention of triangles being really bad, but not sure why and in another I saw a techniqued for moving stars down the axis of the model but again, not sure why.

Obviously tsplines wants 4 sided polygons but why are triangles undesirable?

In one model I am battling with stars. I have two and they throw all kinds of wierdness into the smooth lines. Also when selcting edges and the hitting L to select the line, it stops at the star, probably becuase it doesnt know which direction to continue. Thats fine, but how else do stars affect the model and how do you deal with them?

Finally, I am having a really tough time modelling a complex shape in 3 dimensions that has several curves that must intersect at 45deg (or there abouts)

the problem is that the majority of the model runs longitudinally but a major surface cits through the square mesh body at 45deg. I do not want to convert to nurbs because there is a lot of work to do in Tsplines with the design. I also have another major feature that branches off this main line at a very shallow angle (forming a triangle) much like train tracks branch off. This line then rejoins the main line in similar shallw angle.

I cannot figure out how to model this with squares. If I drag two sides to become one flat side, leaving the other two sides to form a triangle, the smoothing of all that throws all kinds of wierdness into the model.

Finally, how do you introduce an edge from a nice curved line normal to a number of parallell edges. Can you project an edge onto a Tsplines model like in Nurbs?
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Re: T Splines Stars and five sided polygons

Postby JSantocono » Tue May 24, 2016 10:04 am

Hi Proterio.
Proterio wrote:Obviously tsplines wants 4 sided polygons but why are triangles undesirable?

Proterio wrote:I am still not clear about what happens within TSplines when you end up with a star (the intersection point of five lines) and polygons that do not have four sides ie triangles and 5 sided "squares".

StarPoints are a key element on T-Splines surfaces. It is what makes possible to make complex surfaces with smooth transitions. You are correct, it allows multiple intersections in a single point.
Ngons (3, 5, 6,... sided faces), are in a way StarPoints too. You can not see them, but you can notice that when you convert a NGon into Nrubs, the surface will be split inside the face, just like a StarPoint does.

Proterio wrote:Obviously tsplines wants 4 sided polygons but why are triangles undesirable?

Triangles are undesirable because they are difficult to control. That doesnt mean you can not use them. The problem is specially when you have tinny triangles in curvature transition areas. It can produce winkles that you can not control (As I said above, there is a StarPoint inside).
Also, NGons, as StarPoints, makes the surface "heavier" for calculation and can slow things a lot. And when converted to Nurbs, result in more surfaces.

Proterio wrote:In one model I am battling with stars. I have two and they throw all kinds of wierdness into the smooth lines. Also when selcting edges and the hitting L to select the line, it stops at the star, probably becuase it doesnt know which direction to continue. Thats fine, but how else do stars affect the model and how do you deal with them?

Correct. StarPoints are LoopSelection dead ends. As you said, there is no way to know what direction you want the loop.
Not sure the reason you get wierdness on your model, but it can basically be two things:
-You need to "relax" the surface by making it uniform. Just run the T-Splines tsMakeUniform command.
-You have T-Points too close to StarPoints. T-Points need to be more than 2 faces away from StarPoints in order to not be influence by it. Using T-Points and StarPoints on the same area can be tricky. You need to know the "rules of engagement" (You can check the T-Splines Manual). I dont recommend doing this for new users.

Proterio wrote:Finally, I am having a really tough time modelling a complex shape in 3 dimensions that has several curves that must intersect at 45deg (or there abouts)

Difficult to say without seeing the actual model and topology... Can you post it? I am sure there is a solution.

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