I am trying to get a basic Spline IK setup going, just to understand how Houdini does it. I create a geometry object, delete default file and then create a NURBS Curve SOP.

Then I go back up to /obj, switch to Character, and click Bone. I set the solver to Follow Curve and create 4 connected bones, and hit right click.

Now, where do I tell this chain that its Curve1 that I want it to follow? I found an old Houdini 3 tutorial that has a field in the Bone tab of the bone OP property page which lets you chose the curve, but all I can find similar in the new version of Houdini is a Path parameter, but that doesn't seem to be doing what I want it to do..

Also, the docs don't seem clear on this, or maybe they do but its hard to search at it when everything is in PDF format, so I'm hoping someone can set me straight in a heartbeat.

Thanks…

Once you have built a curve, select Follow Curve Kinematics in bones mode and create the bone chain. After you right click to finish the chain, Houdini should ask you in the help bar to select the curve to use for the kinematics and right click, so select the curve object and right click.

Here's what I do, though. Create the bone chain or the whole skeleton if you like with No Kinematics. While sill in bones mode, select your IK type from the top of the viewport, then control and right click and select “Add Kinematics”. Add all the kinematics you want, just follow the prompts in the help line. That's the blue bar at the botto of the interface in Houdini 6, or at the top in 5.5.

You can also change the curve object in CHOPs by looking at the properties of the KIN_CHOP for that particular IK chain.

There's actually some rigging tutorial videos at www.3dbuzz.com for Houdini, and one of them shows you how to make a simple spine.

Michael, Thanks!

I'm embarrassed that after finishing the chain I never checked the status bar to see Houdini requesting me to click on the curve for it to follow.

In my own defense, I do think its wierd that at this point, after the chain is done and you are supposed to select the curve, that the cursor still has the chain drawing icon, as opposed to the traditional Houdini selector arrow icon..

Not to make excuses, doh on me, but still it would be a helpful cue that a new type of selection or action is in order now for the user to commit.

Thanks for your answer though and I am not sure about your method though. I understand how to do it, but what is the benefit? That you can chose the solver type later and not worry about it up front?

I'm sure there's more to your method I am being obtuse again.. Maybe its too early (or late rather) for me to be doing this stuff but its the only chance I get

Thanks again Michael..

By the way, now that I think about this I'm not sure Follow Curve is really what I want.

I guess I was hoping to now grab the end effector of the chain and have IK so that I am able to pull it around and have the chain and the Curve along with it follow along.

Is follow curve what I want for this? I know I once did this in Maya but I forget the exact terminology.

IK, and FK solvers will give you end effectors you can grab to move bones or chains of bones around. You'd use Follow Curve IK to do long snaking bone chains like spines and pony tails and tails. To be able to modify the curve, you'll have to create the equivalent of a cluster in Houdini. Go into your curve object and apply a transform SOP to each curve CV or groups of curve CVs and enable their handles. Alternatively, you could just apply the transform SOPs and then create Nulls at the OBJ level for each transform, then link them to their respective transform SOPs using channel references. The video tutorial I mentioned explains the former method.

Oh, and what I explained isn't “my method”, it's just another way to do it. There's nothing to it. It just makes more sense to me to put the whole skeleton together (well, half because you can mirror it) and then do all the IK, and then rename all the IK handles and CHOPs, then mirror, then build controls.