modelize a peak (facet) on cylinder

 From:  Michael Gibson
7106.2 In reply to 7106.1 
Hi Finema, typically you would do it by incorporating the peak into your profile curves that you use to construct the base shape, for example lofting through a set of profiles like this:



With curves like that, you can then run Construct > Loft to build the "peaked" cylinder form:




For making a smoother shape it can be good to use the "Loft style = Loose" option in Loft, that makes the surface to be more gradually guided by the profiles which makes for a more gentle result rather than the surface being forced to go exactly through each profile curve.

But typically in NURBS modeling you would usually focus on forming profile curves for your desired shape and construct it more directly like this. You don't usually do what you see in polygon modeling where you start with a plain shape and then push and pull directly on the 3D surface to modify it, although it is possible to do that to some limited extent.

If you want to do some point sculpting type approach, start with your base cylinder and use Edit > Separate on it to break it apart into individual surfaces. You can then turn on control points for the cylinder surface using Edit > Show pts, and use Edit > Add pt to add more points to localize the effect of moving them. This type of surface control point modification can be used in MoI for certain cases, but it's not normally the main way used to create everything like it is in a polygon modeling program - with NURBS modeling you can't just add in one single isolated point somewhere to add detail, you have to add in an entire row or column of points at a time since a NURBS surface is always defined as a row and column grid of points.

So typically with NURBS modeling you do things by creating profile curves and then construct your final 3D shape directly from those. If your protrusion is very localized you build it as a separate part and then use filleting or blending to connect it to the base form.

- Michael