T-Splines / Imagine & Shape

I’m a bit unsure how these work. Am I right in saying that T-Splines uses Sub-D modeling and is not actually NURBS. So therefore it is polygon data which can be converted to NURBS later?


Then how about Catia’s Imagine and Shape. Does this use Sub-D modeling and NURBS surfaces?

Please post links if you can.

Hi, I’m a developer for T-Splines. Saw this come up on my alerts, figured I’d give a quick response… :slight_smile:

Sub-D modeling is used in Maya, T-Splines, and Imagine and Shape, and they all need to keep a control mesh around to work on. They all convert to NURBS when requested. The conversion can’t be exact near star points (extraordinary points), for mathematical reasons.

T-Splines for Rhino converts to NURBS for display, so anytime you’re looking at a T-Spline, you’re actually looking at the NURBS conversion (you can toggle this option for speed if you want). I imagine that Imagine and Shape is doing something similar, but I honestly don’t know. Maya only converts when you run the convert command, and most of the time is successful, although there are a few unusual cases where the conversion fails.

The main difference with T-Splines is that the surface type is compatible with degree-3 NURBS - that is, you can convert any untrimmed degree-3 NURBS to a T-Spline, and it remains exactly the same shape, with the same control points in the same positions. Then you can take that shape and do Sub-D style modeling with it, extruding faces, etc. You can also have rows of control points that T-off, stopping abruptly while keeping a well-behaved smooth surface. So, you’ve got more options for how to lay out your topology. In terms of NURBS compatibility, any command that takes NURBS surfaces in Rhino will take T-Splines as well.

I think Imagine and Shape’s main advantage is that they deal well with trimmed surfaces, and they’re integrated with Catia. But I’ve never been able to try Imagine and Shape, so I don’t really know.

Again, I’m obviously biased, but this is my understanding of how the surfacing technology of the three products compare. Hope it’s helpful… :slight_smile:

Thanks for the info Tom. So in essence you’re working on a polygon cage which is being converted live to Nurbs (maybe it goes from polygons to a sub-d to a Nurbs conversion?).

Do you get exactly the same result with a surface contaning a T-Off compared to one that doesn’t?