Why doesn't Noise SOP work on Line Sop?

Hi guys,

this issue has confounded me for a while. Why doesn’t the noise sop work on line sop when the noise sop is set to point position?

Thank you.

Yeah that seems strange, might be a bug. I’ll ask the programming team if there is a reason for it.
NoiseSOPSingleLine.toe (4.82 KB)

Here is an example based on Matt Daly(FB)'s suggestion, where he suggested I add normals to the line.

Again, what’s strange is when I use attribute create to add normal, nothing happens. But if I use noise sop to operate on normals and attach to it just a normal Line sop, I see movements in the color of the line.

It’s only when I use point sop to add an arbitrary normal, did the noise sop start to work.

Matthew Ragan also noted this issue in one of his videos. He ended up using a noise chop to drive the point coordinates via a chop to sop.

Looking forward to a solution/explanation to this issue.

Thank you.
LinePointNoise.toe (3.93 KB)

Okay I think I figured out why. From the Noise SOP help when set to Point Position : “Noise is applied in the direction of the point normal. If no normal is specified, a normal is computed.”

So the the question is why the Attribute Create SOP doesn’t allow it to work, or it doesn’t work on just a standard Line SOP when the Noise SOP should calculate the Normal? In these 2 cases where the normal is calculated, since there is no ‘direction’ of a single line, normal is calulcated to be 0, 0, 0. It seems when normal value is zero no offset is applied by the Noise SOP.
LinePointNoise.2.toe (4.02 KB)

Ahh ok. That makes sense.

Unfortunately, the documentation you quoted was collapsed. Took me a sec to find that line. And your explanation as far as why attribute create doesn’t work makes perfect sense as well.

I think what confused me was when I changed it to operate on normals, there were movements. How were those normals calculated? Because technically line sop doesn’t have any normals.

Anyways, thank you for clarifying this.