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How to keep the length of an animated curve constant? (or stop points

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I'm having a problem with a setup I'm trying out and I'm hoping someone might have some ideas on what I can do?


I'm creating this 'archway' that's made out of spinning blocks. The blocks are moving along the path of the archway. (At home right now, I'll put an explanatory pic up when I'm back at work tomorrow.)

For this animation the archway is constantly changing it's shape.


To acheive this whole look, I have about 6 nulls which I animate the positions of. Then

-create a closed curve through all the nulls.

-carve along the curve (this is what makes the cubes travel along the path)

-resample the curve

-sweep and skin a circle along the curve to create a tube

-scatter points on the tube

-copy boxes to all these points.


This works reasonably except when the curve changes length and then the scatter sop ( or maybe the point numbering of the tube ) changes and all the  boxes jump to different parts of the curve.


I'm not sure what to do about this. My current idea is to try and keep the length of the curve constant. -Two of the nulls and the bottom part of the curve are off camera. I am thinking I could use a measure sop and a Python expression to iteratively reposition these two off-camera nulls to maintain a constant length. I've had a go, but my Python in Houdini is pretty beginner and I'm not having any luck yet.


Any suggestions?



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Are you resampling the curve by lenght? If so try it with a fixed number of points.



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