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View Full Version : LW Curve Types? Please enlighten me...!



Marander
06-23-2015, 01:50 PM
Hello

I'm a bit confused by the different types of curves / splines / lines in LightWave. In what situation do you use these different types? For example for: Rail extrude, exact spline modeling, spline control in Layout etc.

So far I have just used single points, then connect them to an open curve (for example to rail extrude cables etc.).

What are the advantages of the new LWCAD5 splines? I understand NURBS can provide more accurate modeling than subdivision / catmull but LW had spline patching since years if I'm not mistaken. Is there types of curves I should avoid? Why are there even 2-point polys and how do I make them round like curves? What's the correct way to create 2-point polys from scratch or from objects? The action Create Poly Chain doesn't seem to do what I expect.

I must say, LW is not intuitive or logic in these subjects at all to me.

Sorry for the plenty questions. Please enlighten me...! Attached a test of different curve types in Modeler.

Thanks!

128688

128687

Edit: Is LW OpenCurve then same as LW Spline? Is there a way to display / differentiate the types of objects in the modeler viewport (statistics panel shows the curves but not LWCAD ones)?

prometheus
06-23-2015, 05:34 PM
Hello

I'm a bit confused by the different types of curves / splines / lines in LightWave. In what situation do you use these different types? For example for: Rail extrude, exact spline modeling, spline control in Layout etc.

So far I have just used single points, then connect them to an open curve (for example to rail extrude cables etc.).

What are the advantages of the new LWCAD5 splines? I understand NURBS can provide more accurate modeling than subdivision / catmull but LW had spline patching since years if I'm not mistaken. Is there types of curves I should avoid? Why are there even 2-point polys and how do I make them round like curves?

Please enlighten me...! Attached a test of different curve types in Modeler.

Thanks!

128688



128687

Edit: Is LW OpenCurve then same as LW Spline? Is there a way to display / differentiate the types of objects in the modeler viewport (statistics panel shows the curves but not LWCAD ones)?


I wonīt go in to differences between lw cad splines or true arts bezier or pictrix bezier, I am sure some of them share underlying tech but are implemented to work differently.

I think I could say there are no direct difference between lightwave spline draw and lightwave open curve, except for how you create them, create open curve creates the same spline type as with draw spline, but draw spline creates it directly with some control..and create open curve creates it based on selected elements such as points.

I think it is the similar with two point polychain and line pen, you create two point polychain by previous selected elements and the end result is a two point poly chain, with line pen you create it directly without previous selected elements.

The bezier curve has control handles for edge controls wich is a little different than the standard spline tool, but once dropped I think they are the same in curve type..depending on amount of divisions of course.

the other spline types like lw cad and senseis, I think are non destructive..wich means you should be able to pick them up again and work with them with weighting(edge sharpness)...not sure about them though.

line pen or two point polychains, most used for dynamic stuff and previously also for fiber fx rendering, spline curves canīt be used in layout dynamics..and not long ago they couldnīt be used to render fiberfx(I think that is possible now though)
two point polys also renders directly in lightwave ..so that can be used to create lightning bolts or other effects.

Sensei
06-23-2015, 06:47 PM
What's the correct way to create 2-point polys from scratch or from objects? The action Create Poly Chain doesn't seem to do what I expect.


f.e. draw spline with Sketch,
then use EasySpline's Spline Density http://www.easyspline.com
to quantize spline to equal length segments,
then select edges in Edge Mode,
ctrl-c,
ctrl-v, to 2nd layer,
And you have chain of 2 point polygons.
It could be then used in f.e. hair rendering plugins,
or directly rendered by LW renderer (splines are not renderable).

Catmull-Rom curve is the only built-in curve type.

LW Bezier tool is generating Catmull-Rom curve. So basically freezing Bezier to Catmull-Rom.
After dropping tool, it's just Catmull-Rom.
You can have all-the-time Bezier, using mine TrueArt's Bezier,
available to download from http://www.trueart.eu
You can save object for later use in this mode,
and it remains Bezier,
until freezing,
or using directly in EasySpline.

Catmull-Rom curve - curve is passing through the all control points.
Bezier curve - curve is just approaching control points (thus it looks more smooth). Passing them only at 1st and last point. This allows less control points to have smoother look.

Marander
06-24-2015, 01:59 AM
Prometheus and Sensei, thank you very much for your explanations. The TrueArt tools seem indeed very useful.

meshpig
06-24-2015, 02:44 AM
I don't know about Trueart's splines but LW splines only support a limited number of control points. Used to be 128, post 64 bit it's about 200 but lwcad splines are, it seems open to what your system's capacity is. Correct me if wrong.

Sensei
06-24-2015, 06:23 AM
Meshpig, there is limit of points per polygon, regardless of type of polygon.
Different versions of LW has it set to different value.
It can be read using LWSDK LWObjectFuncs->maxPointsPerPoly field.

There will be natural limit of number of points in IFF LWO binary file specification.

See this, I generated 1000 points curve using Spline Density, built-in LW Catmull-Rom curve:
http://forums.newtek.com/attachment.php?attachmentid=128694&d=1435149305

Some specific tools like Sketch could have their own internal point limits..

prometheus
06-24-2015, 09:02 AM
the free Pictrix px bezier tool is also capable of creating polychains for fiberfx directly when drawing in line mode or use for dynamics, but then again...as from 11.6.2 standard curve splines works with fiberfx too when rendering, but in opposite to polychains, such fiberfx guides will not work with dynamics only rendering.

px bezier has some limits to points too, otherwise it is quite awesome since you can save out curve profiles and load back in and use to create polygon surfaces, line, bezier curves, tube, belt, extend and extrude elements and twist scale etc.

Lightwave seem to have gathered myriads of various spline tools, and soon lwcad new nurbs curves :) maybe someone could make curves renderable too like modo has.

meshpig
06-25-2015, 01:34 AM
Meshpig, there is limit of points per polygon, regardless of type of polygon...

I see, thanks Sensei. So the same will apply to NURBS surfaces.