[Sidefx-houdini-list] basic instancing question

Olex P hoknamahn at gmail.com
Sun Oct 26 06:38:12 EDT 2008


You could render them as Mantra points (using phase functions for
anisotropic scattering if you need it).
This could give you:
1. Simpler setup
2. Good details
3. Super fast rendering

On Sat, Oct 25, 2008 at 8:55 PM, jon parker <parker.jon at gmail.com> wrote:

> Thanks for the repsonse...
> A colleague also tipped me to using displacement mapping to add detail
> to volumes, and it works really well.  For general volumetric
> rendering I'm in agreement with all of the things below.  With what I
> have been tasked with, there is a large scale difference in the nebula
> as a whole, versus the details we're trying to show... there are a
> large number of tiny 'knots' in the nebula that need to be in the
> right place according to some astronomical observation data I've been
> given.  My first attempt was to birth metaballs from the right
> locations and render them volumetrically, embedded within the rest of
> the gas volume.  But the shading quality of metaballs doesn't seem to
> be as nice as I hoped.  In fact I ran a test where I converted them to
> a massive image3d texture, and the shading quality was much nicer, but
> generating it took forever and that really hinders that technique for
> testing.  So my latest idea is to use a lot of knot-shaped volume
> instances, and displace them in world space to add variety, but they
> seem to be displaced before they are instanced, and not afterwards
> like I hoped.  Any other suggestions towards creating them this way?
> --jon
>
> On Sat, Oct 25, 2008 at 9:01 AM, Pablo Giménez <pablogipi at gmail.com>
> wrote:
> > Sounds pretty good.
> > The dispalcement to do the convection is quite interesting
> >
> > 2008/10/24 Remba, David (Space Technology) <David.Remba at ngc.com>
> >
> >>
> >> I've been working on clouds, and had good results
> >> using simple geometry (spheres, boxed shapes) then
> >> subdividing to round the shapes, then iso-offset to
> >> create a low density volume (20x20x20).
> >>
> >> The good stuff happens in a custom material:
> >>
> >> 1. displacement VOP SHOP uses various noise functions
> >> to push P around (for clouds: only in the up +Y direction
> >> to simulate convection, and using an abs() to make it
> >> puffy looking).  For nebula I would try the built-in
> >> aanoise VOP.
> >>
> >> 2. surface VOP SHOP based from the VEX Volumecloud shader,
> >> and added extra features for clouds to cut off and
> >> darken the bottom.  Higher density makes the gas more
> >> chunky looking, lower values make it more wispy looking
> >> (good for nebulas).
> >>
> >> tips:
> >>
> >> Very important to adjust the Volume Step size to as large
> >> a value as possible (just below the noticeable speckle artifact).
> >>
> >> For fast rendering: try only one or two lights; if you need
> >> more, do multiple render passes and comp them.  Use Ray Trace
> >> Engine, lower opacity limit to 0.9 if the nebula/clouds are
> >> chunky.
> >>
> >> For nebula you might try some glow effects (see the emit
> >> in the VEX Super Material shader).
> >>
> >> p.s. For nebulas, you might try separating very far objects
> >> which are more of a 2D problem, from closer 3D objects.
> >>
> >> p.p.s. I work at a space technology company so I might get
> >> to work on nebulas soon also!  I'd like to hear you things
> >> go for you.  My email:  daveremba at yahoo.com
> >>
> >> I hope this helps,
> >>
> >> Dave
> >>
> >> _______________________________________
> >> David Remba
> >> Tel 310 813 5899 Cel 310 809 6375
> >> Northrop Grumman Space Technology
> >> IMAGE Center
> >>
> >>
> >>
> >> -----Original Message-----
> >> From: sidefx-houdini-list-bounces at sidefx.com on behalf of jon parker
> >> Sent: Wed 10/22/2008 9:13 PM
> >> To: sidefx-houdini-list at sidefx.com
> >> Subject: [Sidefx-houdini-list] basic instancing question
> >>
> >> Greetings esteemed Houdini masters!
> >> I've been tasked to create a planetary nebula by some very demanding
> >> scientists... I've done some lighting for studios using Houdini in the
> >> past, but now the holes in my knowledge about Houdini are showing up,
> >> so I am looking for some basic workflow questions to be cleared up.
> >> For the nebula, the basic gas volume is looking great, however there
> >> are a large number of 'knots' in the nebula that need to be quite
> >> detailed.  I tried using volumetric metaballs first, but these don't
> >> seem to shade as nicely as the volume primitives... the density
> >> gradients don't seem as smooth, and the edge glows just aren't there
> >> like they are with volumes.  Converting them to i3d files gave me a
> >> much better look, but that's quite time consuming during look
> >> development, since I need at least 1024^3 i3d files to maintain the
> >> detail.  So I've tried instancing volumes to each knot, and this
> >> potentially looks best, except I have two questions about it...
> >> firstly, what is the best way to transfer point attributes to the
> >> volume?  Secondly, how can I use world space displacement on an
> >> instance?  On the first attempt I discovered that instances themselves
> >> are not displaced; instead they pick up the displacement of the source
> >> geo before they are instanced.   Aside from this question, which
> >> approach makes the most sense?  There are obviously a lot of potential
> >> paths to take in Houdini.
> >> Cheers,
> >> Jon
> >> _______________________________________________
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> >>
> >>
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> >>
> >>
> >
> >
> > --
> > Un saludo
> > Best Regards
> > Pablo Giménez
> > _______________________________________________
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