I'm working on a problem, and wondering if anyone has tips on how to solve this in Houdini.

The problem is to create a number of N subset curves from a set of P points in a particle system. Given a particle system, I want to randomly select K points (K equals 8 ), then use these points as the control curves for a bezier curve. The curve should select an initial random set of points, but keep those same points as the particle system animates. This curve object is repeat N times, using different random points, to create N unique curves that move and distort based on the particle system.

Any suggestions on the best way to approach this?

I would sketch out just exactly what you want to have happening. A good sketch helps you see your project in a different light.

Just reading it, kind of sounds like you want a bunch of splines floating around in space based on the particle locations, like noodles in water?

What are you planning on using this for?

Download the FX Tools from the shelf then have a look at the wispy smoke tool. It does a pretty elaborate job at skinning particles. It even supports non-ordered birthing of points and points that are killed prematurely

As for connecting the points with the Add SOP (there really is no better way) you can use the expression field. Attributes that are commonly used to skin particles:

If you are birthing from points in the Source POP, you can add an attribute on the source geometry for each point and use that in the Add SOP to connect the points.
You can use the “parent” attribute on split particles to connect the points.

It is trivial to convert the polygon curves in to Bezier curves but I would rather go to NURBs as Bezier's need to have n-ordered curves or will fail.

add an attribute on the source geometry for each point

I assume that the Add Sop will connect all groups of points that are in the same group (group attribute is equal). How do I set this attribute so that a random subset of 8 or so particles gets its own group? Would i need to use an expression for that?

Thanks for the replies.. -R

You can type in any expression in to that field to create the logic to connect the points.

I prefer to create an attribute with an Attribute Create SOP on the points before the Add SOP to build the logic to connect the points. You will have the attribute mapping present so you can just type in the attribute name directly and the points with the same attribute will be connected together.

Its working, Thanks!

popnet -> attribcreate -> add sop -> convert (to nurbs)

Here's the proof.. I also wrapped the subset curves to a sphere, and lofted them to create a “woven sphere” look, my final goal..

instead of using the Sweep method, try polywire