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HOWTO: Creating Motion Paths

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Here's a quickie on how to create a motion path object for a moving object. Basically, it takes all the positions of an object over time and creates a line through them. It may not be obvious to new users of Houdini so I thought I'd take some time to show how to do it. This can be done either before, during, or after animating.

1. Go to CHOPs, and put down a Fetch CHOP. Set the following parameters -

OP: obj, Path: set this to the name of the object you wish to create the motion path for, Ignore the second Path parameter leave it at none, Channels: t[xyz]

2. Go to Objects, put down a new Null object. Inside this new object, delete all the existing sops and put down a Line SOP. Under the Points, put in the expression $F. This means that the line will draw frames 1 to your current frame number on the playbar.

3. To the Line SOP, append a Channel SOP. Set the Channel SOP's parameters to reference the CHOP we created in step 1.

That's it. Now when you key the animation of your fetched object, a line will be traced through from frame 1 to your current frame. If you want more of the path shown, you could try using $F+24 instead to show a bit of the future or use $FEND for the entire length of the animation. Since we created the path geometry inside a Null object, it shouldn't show up in rendering. Finally, if you wish to see that path inside other objects, you could turn on its Xray flag (right-click on the path in the object viewer).

What do you think?

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Hey Edward

Quite frankly, I don't think that that will be apparent to alot of experienced Houdini users either :). Its one of those things that seem possible in Houdini, but will take some thinking to get it right. So thanks for that.

BTW, theres still something wonderful missing from that you know? It would be awesome if it would place a null at every keyframe point which you could then drag around in the viewport to move the position of the keyframe :D.

Now that I think of it, that might be possible too... If only I had more time B)



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