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"Rune" <run### [at] mobilixnet dk> wrote :
>
> I tried to follow some of your suggestions, and this is the result. I
think
> it's better, but I can still use some more suggestions for improvement. :)
I actually watched some grass this afternoon, and my grass doesn't bend
in the middle unless it is a typhoon. It bends along it's whole length
somewhat. And in the size range of what you have, only one gust would fit on
the screen at the time.
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"Bill DeWitt" wrote:
> I actually watched some grass this afternoon,
> and my grass doesn't bend in the middle unless it
> is a typhoon. It bends along it's whole length
> somewhat.
My simulated grass also bends along its whole length. Actually, it's just a
simple parabolic function. (In the last animation it was linear.) One side
effect of the method used is that the blades get longer the more they bend,
but that's just one of the compromises of this simulated grass...
> And in the size range of what you have, only one
> gust would fit on the screen at the time.
Hmm, ok. But won't it looks wrong if all the blades bend in the same way at
the same time? Maybe not...
Rune
--
3D images and anims, include files, tutorials and more:
Rune's World: http://rsj.mobilixnet.dk (updated Feb 16)
POV-Ray Users: http://rsj.mobilixnet.dk/povrayusers/
POV-Ray Ring: http://webring.povray.co.uk
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I did a little observation of my yard today and I found out some interesting
things about grass movement.
First, only the longer blades bend very much, and when they do, it is really
a complex sort of movement.
Second, the movement has two distinct components- bending and oscillating.
When the wind blows over longer stalks or leaves, they tend to bend gently over
the length, pretty much as the parabolic bending in your model. It may actually
be a catenary curve due to the forces and loading, but that is a small thing.
But the oscillating movement is a side to side twisting, more rapid for
shorter blades than for longer ones. The oscillation period is much shorter
than the bending or waving period. The wind moves in "swells" over large,
curved or crescent shaped areas, exciting the stiffer stalks to oscillate more
and the thinner or longer ones to bend and curve.
This is way too much complexity I think for the model you have. The texture
itself looks great as it stand; getting realistic looking movement may be far
harder than it is worth right now.
If I were modelling grass and leaves in the wind, I would attach masses or
springiness to control points and apply forces against them. Otherwise, the
movement tends to look more like seaweed drifting in the water, which is
essentially what your texture may naturally tend to emulate. Don't give up; it
already makes nice turtle grass for undersea animations!
Cheers!
Chip Shults
My robotics, space and CGI web page - http://home.cfl.rr.com/aichip
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"Rune" <run### [at] mobilixnetdk> wrote in message
news:3ca51209@news.povray.org...
> "Bill DeWitt" wrote:
> > I actually watched some grass this afternoon,
> > and my grass doesn't bend in the middle unless it
> > is a typhoon. It bends along it's whole length
> > somewhat.
>
> My simulated grass also bends along its whole length. Actually, it's just
a
> simple parabolic function. (In the last animation it was linear.) One side
> effect of the method used is that the blades get longer the more they
bend,
> but that's just one of the compromises of this simulated grass...
Maybe that's it. It looked a little springy to me. And I think it really
bends too much, it almost looks like seagrass.
> > And in the size range of what you have, only one
> > gust would fit on the screen at the time.
>
> Hmm, ok. But won't it looks wrong if all the blades bend in the same way
at
> the same time? Maybe not...
No, the gust would sweep across the view, and when one was partly off,
another would be partly on.
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> I tried to follow some of your suggestions, and this is the result. I think
> it's better, but I can still use some more suggestions for improvement. :)
Cool, dancing grass!!!
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Thanks for all the suggestions everyone, but I think I'll just drop adding
support for wind.
Rune
--
3D images and anims, include files, tutorials and more:
Rune's World: http://rsj.mobilixnet.dk (updated Feb 16)
POV-Ray Users: http://rsj.mobilixnet.dk/povrayusers/
POV-Ray Ring: http://webring.povray.co.uk
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"Rune" <run### [at] mobilixnetdk> wrote in message
news:3ca58c1b$1@news.povray.org...
> Thanks for all the suggestions everyone, but I think I'll just drop adding
> support for wind.
Aw... Oh well, it was fun to think about.
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> I tried to follow some of your suggestions, and this is the result. I
think
> it's better, but I can still use some more suggestions for improvement. :)
I don't think the grass bends over all at one time, the wind gusts over
moving across.
__________________
RAY
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Sir Charles, that's a pretty good description. From what I've learned about flight I
would modify your outlook by describing the
motion as drag, in addition to a force and reaction. In other words, the wind blows
about the blades, and the drag of the blades
creates pockets of varying pressures. The grass blades proceed toward the lower
pressure zones, which move, and thus appear to be
waving in a random manner. Direct gusts appear to overpower the effect of low
pressure, but overall it is the disparity of pressure
that causes the majority of motion. Turbulence must be considered as well...
turbulence from surface perturbations.
You could also say the blades are getting sucked around, rather than blown. :)
Grim
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That's a shame, because you are onto something here.
Grim
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