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I know that Beziers, Nurbs curves and Paths have different controls:

  • Bezier handles have control over tangents, and the curve always touches the control point.

  • Nurbs curves don't touch the control points, they just bend towards them. The curve doesn't reach the first or last control points, but ends around the second/second-last point.

  • Paths are the same as Nurbs curves, except the curve continues to reach the first and last control points.

But what are the practical differences between them? What can each of them be used for that the others can't, or what about each of them makes them easier to use for certain tasks?

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    $\begingroup$ that can help ? blender.org/manual/modeling/curves/… $\endgroup$ – lemon Jul 27 '16 at 10:14
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    $\begingroup$ See blender.stackexchange.com/questions/56713/… for the best possible answer. $\endgroup$ – metaphor_set Jul 27 '16 at 10:15
  • $\begingroup$ It would be much better to ask just about their differences, and let the practical applications to the user. Because it is dependent on the thing you want to do. For different situations different curve types fit the most and to name all the situations is much harder than to name just the curves differences and let the user to understand them, let him think with own head and apply the knowledge to specific practical tasks. $\endgroup$ – Jaroslav Jerryno Novotny Jul 27 '16 at 11:29
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    $\begingroup$ Knowing the differences is easy. Knowing what difference those differences make is a matter of experience and trial+error. I was hoping someone could summarize some of the common applications of each curve type in an answer, explaining why it was best for that case. $\endgroup$ – Greg Zaal Jul 27 '16 at 12:28
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I must say that I make quite extensive use of Bezier Curve objects in Blender, I use them a lot more than I actually use mesh objects.

I work mainly in architecture mostly doing archviz, design and interior decoration projects. I know this is not a popular nor a 'standard' modeling technique, I am perfectly aware how exotic it is and that most people's workflow is far different from mine, even in similar business areas.

Curve objects in Blender suffer from severe limitations when compared to meshes, like limited availability of modifiers, poor texture mapping capabilities, can't be unwrapped, can't have particles or participate in Boolean Operations, and can't be rigged or animated like meshes do.

That being said I find that bezier curve objects kept live and without converting to mesh have certain advantages and also particular constraints that make them well suited for these use cases.

Bezier Curves

By being inherently bidimensional, bezier curve objects (in 2D Mode) automatically guarantee a flat 2D surface avoiding dealing non planar surfaces originating from unintentional snapping, which is a frequent requirement recreating real world situations.

Because they you don't have to work with faces directly, you don't have to worry about topology nor maintaining a good edge flow, like you would with mesh objects. This lifts a huge burden and frees you from worrying about mico-managing geometry.

Since curves have a builtin quality setting for curved segments smoothness you also don't have to use Subdiv Modifiers which are often a source of concern for topology. Mixed straight and curved shapes live happily together automatically handled by the bezier curve fill engine as well; so you also avoid having to worry about adding support edge loops or unwanted smoothing in straight areas.

Because the fill engine also handles automatically inner curves and recursive shapes inside shapes it easily creates holes and islands inside outlines, avoiding extensive use of Booleans, which are slow, error prone and often source of frequent problems and frustration.

The builtin beveling, offsetting and extrusion features allow for a non destructive workflow, which can easily go back to and change parametric without having to redo manually.

Bevel objects also allow defining extrusion shapes along complex paths, common in metal work, frames and railings frequently found in architecture, and often provided in CAD format by manufacturers.

In building and construction area, Bezier curve objects end up being very versatile in designing:

  1. Building walls, which can conveniently be defined as an extrusion of an architectural plan outline that is often provided by the client, guaranteeing planar closed shapes.
  2. Facades, curtain walls, and elevations can also be easily defined from client provided elevation drawings, since again they are mainly bi-dimensional extrusion structures with holes and island that are well defined from a 2D closed curve with holes for windows, doors, openings and stonework around them.
  3. Pavement or floor finish areas (like an room with a certain type of wood, carpet or ceramic tile finish) which often a closed boundary combining complex shapes with mixed curved and straight geometries.
  4. Concrete slabs, or extensive ceilings with arbitrarily shaped and numerous openings for lighting and holes for installed equipment, are also easy to define because you don't have to worry about topology, manually deal with gaps, fill holes nor use booleans.
  5. Railings, metal work, extrusion profiles and frames along complex paths are easily handled by the builtin Bevel objects.
  6. A lot of other real world objects made from sheet materials (like table tops, wood board, wood furniture benefit from the same advantages like easy extrusion, tessellation and beveling.

Other than that, they are also very useful as complement for illustration based graphical design type of work, like Logo design and symbol creation, or 2D type of motion graphics often used in TV, video and animation work.

NURBS

NURBS surfaces on the other hand are more suited for smooth almost organic-like shapes used in vehicle design like cars, boats, airplanes, or more aerodynamic industrial design objects.

They differ from subdivision surface because you never deal with faces directly, the emphasis on precision, trimming, and Boolean operations.

Looking at Blender alone it's hard to imagine using them as an actual full features modelling tool, since Blender's NURBS tools are admittedly a stub, with very limited features and lacking tools.

They are there more as a remnant of the past than as an actual production ready tool. Other dedicated software like Rhino, MoI, Katia, etc. have actually usable and full featured NURBS modelling tools, capable of very accurate surface definition, surface trimming, Boolean operations, etc.

They are very suited for actual technical drawing extraction from models, since correct and exact elevations, plans and sections can be extracted from a NURBS or Solid based 3D model.

Paths

I don't frequently use them myself, but from what I gather they are mostly used for animations purposes, mainly to define animation paths objects must follow, sort like a railway. They are mathematically more accurately and precisely defined, yielding smoother animations and avoiding jitters and sudden movements while animating.

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  • $\begingroup$ Nice examples with the beziers, never thought of using them like that. About nurbs, I was referring to the nurbs curve objects, not the nurbs surfaces. $\endgroup$ – Greg Zaal Jul 27 '16 at 12:47
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    $\begingroup$ Ah yes, I don't think I've ever used a 2D NURBS curve as alternative to bezier. My guess is they are better at defining organic shapes, as opposed to mixed or straight-segments curves with beziers. Also depends on the desired actual shape of the curve, as you mentioned with bezier you define pass-through points, and with NURBS you refine tangents. $\endgroup$ – Duarte Farrajota Ramos Jul 27 '16 at 13:04
  • $\begingroup$ Aren't bezier curves and nurbs curves mathematically the same thing? $\endgroup$ – June Wang May 19 at 15:15
  • $\begingroup$ Not sure about the internal workings, but I've heard paths are more accurate. In practice the way you control them is also different, one passes through points, the other is "fit through". $\endgroup$ – Duarte Farrajota Ramos May 19 at 19:07
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Think of Bezier curves like nurbs, but on steroids. But as we all know, steroids can get you into trouble!!! There's a great film on youtube (link below) that shows that they're actually kinda like the same thing as N curves.

You know that first, 4 point N curve you get when you first create it? Well, just think of B curves like a whole series of those, joined together. Once you start to see these "troughs" in your B curves, it makes it much easier to manipulate them how you want!

https://www.youtube.com/watch?v=Qu-QK3uoMdY

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You guys are so wonderfully technical. LOL. For me, the practical difference between the two types of curves in my artwork is that the N-curve lets me put the vertices of the curve exactly where I want them. The B-curve is for me madly confusing making those curves end up in the right place. It may seem tedious but I will almost bet that I can beat anyone time wise creating a complex of curves using the N-curve, extrude, click (rinse and repeat)like a little race car running around the contours of my design.

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