Hi Houdini dudes,

I like to model stuff. I want to learn how to model in Houdini properly. I switched from using 3ds max to Houdini about eighteen months ago but so far have not really modelled anything complex in Houdini as I've been concentrating on effects work. In max I modelled a couple of cars and a few characters. For character stuff I always used sub-D/box modelling techniques, for which all of the equivilant tools I am familar with in Houdini. The problem is spline based modelling for stuff like cars. I've used the curve SOP a few times and found it quite frustrating, things like being unable to select and move multiple points at a time and not being able to have corner CV's and bezier CV's on the same curve etc. These little gripes leave me wondering how easy it would be to do spline based modelling in Houdini. Do you guys have any tips and/or links to Houdini spline-based modelling tutes/FAQ's?

Any help is greatly appreciated.

Cheers,

Deano.

yeah I'm in the same boat with Max/Houdini. I'm guessing Houdini would have much better Nurbs capabilities than Max but I haven't sorted out the spline stuff yet … any general tips on spline modeling with Houdini

Yeah, spline based modeling is like the superb side of modeling in max, is there any parallel process here in Houdini? It would be amazing to have operations like fillet & chamfer in a procedural flow, leading to unprecedented editability
Max user here too (looking to migrate!!! )
Cheers!

Moving multiple points…Once you select multiple points, hit the “t” key and you will get a translate handle (you can also scale and rotate)which will lay down an edit sop so this is for sure doable. Once you have edited you can always go back to edit sop and hit enter.

Depending on the degree of your curve, corner points are made by laying points on top of points, not sure about Max but this is how it is done in Maya as well. You can also use two curves and a joinSop.

There is also a filetSop, trimSop and most other necessary nurbs tools

The real power of Nurbs in Houdini is the ability move between Nurbs and Polys while keeping the same continuity if you choose, as well as the ability to procedurally generate a lot of curves.

It would be nice to have Max's Surface Tools in Houdini (Cross Section and Surface):

Is that like Maya's birail tool?…not sure how that performs in Max. Looks like nice surfaces tho'

No it's not. Skin SOP can already do what Birail does. These modifiers in Max are collectively known as Surface Tools:

http://docs.autodesk.com/3DSMAX/15/ENU/3ds-Max-Help/index.html?url=files/GUID-1456D1B2-7B31-4894-AC2C-A2F60660C922.htm,topicNumber=d30e102492 [docs.autodesk.com]

http://docs.autodesk.com/3DSMAX/15/ENU/3ds-Max-Help/index.html?url=files/GUID-1456D1B2-7B31-4894-AC2C-A2F60660C922.htm,topicNumber=d30e102492 [docs.autodesk.com]

It involves creating a spline cage and the Surface modifier surfaces the spline cage. It takes a ton of time to model the cage though.

Max also has a Birail tool (2-Rail Sweep Surface):

http://docs.autodesk.com/3DSMAX/15/ENU/3ds-Max-Help/index.html?url=files/GUID-1456D1B2-7B31-4894-AC2C-A2F60660C922.htm,topicNumber=d30e102492 [docs.autodesk.com]

The problem is the final geometry is NURBS and when you convert it into polygons, you end up with a very messy tessellation that's not suitable for subdivision surfaces.

I wrote a tool back in the day that works like the Skin SOP that supports 2, 3 and 4 curves and outputs an all quads polygon surface that's very light and suitable for subd to produce super smooth surfaces. You could model a car body using less than 1k polygons and Catmull-Clark subdivide it 3-4x that looks super smooth in the end.

I find this works better as you don't have to create the intermediate pieces in the spline cage, so the final surface is smoother than you could make it yourself. Imagine this for a car windshield which is very easy to model if you trace the outlines as 4 curves. If you have to connect each point to the point on the other curve, it takes very long and you can't maintain the same smoothness.

You could make your own version that supports a spline cage in Houdini but you would need to connect the pieces cleverly before surfacing each “patch” one by one and then fuse them, etc.

As Pusat mentioned, much of this is in Houdini now. You can draw your NURBs curve cage then panel by panel, take the curves, either carve them up or use CurveSect SOP to cut up the curves and then use the Skin SOP's u and v inputs to get your BiRails patched skin. Nothing has to be exact with the Skin SOP. Close counts but accuracy may suffer but if you are using this as a design tool, loose can be good.

The Skin SOP's feature set allows it to do simple lofts, patches and bi-rails where you can supply minimum 2 curves for u and v or any number of curves for u and v. Very flexible. Mostly works with viewport selections. Actually viewport selections is the only way to do this imho.

As for the types of NURBs curves, their basis is critical. It also helps to refine the carved curves prior to skinning such that at least the u or v cross-sections have the same basis and the same number of knots/cv's to ensure a clean surface. All this can be done in Houdini to keep the surface clean and convert over to polygons.


And that's the real question: NURBs. Why model with NURBs?

Depends on the task imho. If you are creating your own unique car that you want to rework with the base underlying curves, then drawing NURBs curves and creating NURBs patches has a place. Then again with the latest OpenSubD in Houdini and the Crease SOP and the Attribute Wrangle to add specific crease weights to vertices (vertex face points), you have a ton of control to reshape and sculpt.

If you just want to create a digital copy of an existing car or an existing car and then add additional features, sure start with NURBs curves if you wish but then convert over to polygons and make your panels. Or just use the curves as primitive snap guides to help with the box-up modelling.

Skin SOP is just fine with NURBs, Beziers or Polygon curves. You can even mix and match them up for the u and v input curves but that creates some real nasty surface parameterization that will require rebuilding with additional SOPs. All possible though.

I often start with a nurbs curve with an eye towards a polygonal result, but I find that more and more I go curve SOP (set to polygons, with the fewest points possible that give me the result that I need) > fit SOP > resample SOP. I find that this allows me to create nice smooth curves with maximum control and flexibility over shape and parametrization.