Forums Technical Discussion What attribute(s) used to draw Particle Gnomon on screen?

What attribute(s) used to draw Particle Gnomon on screen?

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goldleaf
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I was wondering what attributes are being read, to tell the Particle Gnomon to draw correctly? I'd like to just use that data as a small coordinate system, but I'm confused about where Houdini is reading it from… Obviously, Z is in the direction of velocity, but there isn't any orient or up that I can see.

Thanks!

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fxrod
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That would be the orient attribute.
Francisco Rodriguez
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goldleaf
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Do you know if orient is being calculated behind the scenes or something?

It's not an attribute I can see, or an intrinsic I can find…

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malexander
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It's based on orient, and if that's not present, it uses v, up and q (quaterion) to establish a frame of reference. In your case, it's using just using v.
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fxrod
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It's based on orient, and if that's not present, it uses v, up and q (quaterion) to establish a frame of reference. In your case, it's using just using v.

1. If up is not user-defined, does it default to (0, 1, 0)?
2. I haven't seen the q attribute. Where does this get generated?

All good info.
Francisco Rodriguez
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goldleaf
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In addition to those two questions (thanks Francisco!):

- If Houdini does use 0,1,0 as a default Up under the hood, does that change when Houdini is set to Z-Up? Or is it simply hard wired?
- Is there some preference or variable which allows for writing out these q/up values as attributes? If not, I'll submit an RFE, as that would be super handy
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ben-andersen
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Hey Goldleaf :-)

You might find this helpful:
http://www.sidefx.com/index.php?option=com_forum&Itemid=172&page=viewtopic&t=6679 [sidefx.com]
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goldleaf
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Ah I didn't realize that page (and the one in the docs) had the conditions/recipes!

Thanks Ben!
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