Rhino curves to C4D splines?

[chris_b]

At the moment, C4D can not import 3D splines/curves.
You can, however, get 3D polylines in via DXF version 12.
Your other option is to import a polymesh and make edge
selections, which you can then convert to spline polylines
with the 'edge to spline' command.

One of these days we'll get IGES import, but until then... ;)

[lllab]

oh yes it can!

you can easily export(export selected) splines via dxf from rhino to cinema,
, but i have done that hundrets of times. (maybe you have adjust the standard settings, check them. its calles save as polylines or something)

works very fine, be sure to use dxf 12 or 13 or just use 3ds. in cinema select all the spline and connect them, this makes everything much faster in the viewport.

cheers

lllab

[chris_b]

Hey Illab... if you read my post, you'll see mention that
C4D will bring in POLYLINES from AUTOCAD through DXF 12.
Polylines are not Nurbs curves or Bezier splines though...
so it is only useful if you are dealing with rectilinear geometry
that has no curvature. If you want to bring in real 3D curves
(the kind you'd be building in Rhino) then currently there is
no way in Cinema.... :) Try it...

[Uncle-Ox]

Rhino “curves” (their word for splines)
Hi

I think you're making a slight assumption mistake here. Rhino's curves are true NURBS curves which differ hugely from splines. This would be the same as saying that Rhino's surfaces are in fact poly-meshes (which we ofcourse know they aren't).

C4D doesn't support true NURBS and hence a NURBS curve needs to be converted to a polyline before C4D can handle it. If C4D had supported true NURBS I'm sure not much time would pass before we saw IGES and/or Parasolid import filters created for it.

If you could get someone to write an IGES import filter which converts true NURBS into poly objects that would obviously be awesome since true NURBS are a dream to model with. Untill that time, I fear you'll unfortunately have to do stuff the hard way.

[chris_b]

I bet that if there was sufficient demand, one of the brilliant plugin writers in the community could write an import filter that could import a set of Nurbs curves or other 3D spline curves and convert them to Cinema's internal curve format...

Real Nurbs/Iges support would be great of course, but a simple import filter would be a good hold-over for those that could use it...

In the hand Cinema's spline-handling and 'Nurbs' could use an overhaul similar to the poly-modeling overhaul of R9.

[Per-Anders]

afaik nurbs curves are b-splines (given the name nurbs curve to make it sound rather better than simply one of the more basic curves), remember that nurbs themselves are non rational uniform b-spline surfaces, thus a nurbs curve is in fact an oxymoron as the curve has no surface. i.e. they are the same thing as cinema's own b-spline. any additional functionality found in other packages is purely down to toolset.

[AdamT]

Exactly right. So! You can get exact copies of Rhino splines in Cinema by doing the following: first, make points visible in Rhino. Then, draw a polyline, snapping to the points of your nurbs curve (must be degree 3!). Then export the polyline as polyline dxf (Acad 12), open it in Cinema, and change the interpolation to B-Spline.

Note the note: it seems that Cinema only supports degree 3 b-splines, so if you use a different degree in Rhino you won't be able to match the curve in Cinema.

[Newstream]

Thank you all very much for your responses!
Adam, it worked!
This must mean that Rhino can be used as a “steppingstone” when importing AutoCAD .dwgs into C4D.
However, for this to work, one would first need to install the latest (free) BonusTools into Rhino which happens to include .dwg import /export functionality.
Once imported into Rhino, the lines (which now are curves) can then be exported and then imported into C4D.


Have a good weekend all!
Alex
http://photos2.flickr.com/2119381_c0d2284dec_o.jpg

[Shane W]

Sweet tip adam!

[lllab]

chris b see it works, of course also with curved lines...

its the same as i described. i have do this every day almost! i know about what i talking;-)

cheers

lllab

ps. badtastic, rhino support dwg import export since a LONG time, without the bonus tools,
of course you should update your rhino installation always with the latest service release.
good luck:-)

[AdamT]

Ilab,

Yes, your method works of course. The only advantage of the method I described is that you get the same point count in Cinema that you had in Rhino, e.g., maybe 4-5 points instead of 45-50. A little better if you plan on doing any changes in Cinema. :)

[lllab]

Thats right Adam, sorry

cheers

lllab (with 3 "L"s)

[chris_b]

Polylines to BSplines - splendid tip Adam!
In fact, you don't have to redraw a polyine, but simply rebuild your
curve as a degree 1.

lllab, thanks :) I have been using DXF 12 to bring splines into Cinema
for quite some time also... with lots of extra points *shame*
This Reinterpolation trick is great though! I guess the route back
would be just as simple - converting to linear and then rebuilding in
Rhino as degree 3

I wonder if there is any way to verify the accuracy of the translation?
I am curious how you discovered that Cinema's BSplines are limited to
degree 3? I have always been curious about our selection of interpolation
methods (Bezier, B-Spline, Cubic, and Akima)... not to mention the mysterious
Bezier Nurbs object... I wonder whether Maxon at some early stage in the
development of Cinema considered implementing a Nurbs modeling system?

[AdamT]

> Polylines to BSplines - splendid tip Adam!
> In fact, you don't have to redraw a polyine, but simply rebuild
> your curve as a degree 1.

Indeed, very good point.

> I wonder if there is any way to verify the accuracy of the
> translation?
> I am curious how you discovered that Cinema's BSplines are
> limited to
> degree 3?

Just trial and error--checking to see how splines from Rhino match the interpolated splines in Cinema. As far as I can tell the degree 3 Rhino spline matches the Cinema B-spline exactly.

[Mike Abbott]

Mike Abbotts' bluffers guide to NURBS... ;)
----------------------------------------

OK guys, there is a little misinformation in this thread (as in most others) on the subject of NURBS, so here is a quick summary:

NURBS:
(Non Uniform Rational B(basis)-Spline). This is a particular type of mathematical description of a curve that offers a high degree of flexibility in describing a curves' shape. It's particularly good in allowing the shape of a curve to be adjusted in one place with minimum effect on other places. That's why NURBS are used to define the shapes of all sorts of product designs - from kettles to cars.
A NURBS (cuve) is defined by Control POINTS, KNOTS and WEIGHTS. A NURBS curve can have any degree (degree = the high exponent in the forumula generating the curve).

B-SPLINE:
A B-Spline is a SUB-SET of a NURBS curve. It's like a NURBS curve with equal weights. So, it's controls are POINTS AND KNOTS.

BEZIER:
A Bezier curve is a SUB-SET of a B-Spline. It has equal knots as well as equal weights.

CUBIC:
Is a bezier with a fixed degree of 3 (ie: a 3rd degree bezier).

How these curves are implimented will vary from programme to programme and toolset to toolset. Cinema has minimal control (enough for general use, but minimal if you are into CAD ;). Tools like Rhino and FormZ give you full control over knots and weights so you can generate more sophisticated curves.

So, any curve you make with a Cubic, Bezier or B-Spline can be replicated as a NURBS. But... Cubic, Bezier and B-Splines can't always replicate a NURBS...


HTH - at least a little ;)


Mike Abbott

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