Well, I am interested in modelling wind patterns over a reed field, or a 
corn field. What I seem to observe are turbulent wave patterns moving 
the stalks back and forward while going over the field.

This is a first approximation. I am not really satisfied yet with the 
pattern. What I did is:

1) Make an image_map with a more or less turbulent ripple pattern.
2) Make a height_field based on that image_map.
3) Build a reed stalk with Inverse Kinematic properties (macro with Bend 
parameter).
4) Select random locations on the height_field;
4a) calculate the vertical angle between the normal at that location and 
a horizontal plane (using: VAngleD(V1,V2));
4b) calculate the horizontal angle between (arbitrarily) the +z-axis 
direction (direction of primary bending of the reed stalks) and the 
normal of the random location point (using: VRotationD(V1,V2,axis)).
5a) bend the stalk with a proportion of the vertical angle (4a);
5b) orient the bended stalk by rotating through the horizontal angle (4b);
5c) place the reed stalks at the random locations on a flat surface.

The image shows 15000 reed stalks. About 4.5 minutes render time.

suggestions are more than welcome of course.

Thomas

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> What I seem to observe are turbulent wave patterns moving
> the stalks back and forward....
> I am not really satisfied yet with the pattern.

I think the back part might be why you don't like it.
I don't think the wind would make them curve in opposing directions like that.
I'd say that maybe rather than "height", you use the image map as a force-map.
Better yet would be to use the ripple pattern as "real wind" and translate the
infinite pattern through the stationary reed field.
I'm not sharp enough at the moment to suggest exactly how to do that.
maybe grayscale eval_pigment?
Only bend the reed between 0 and the maximum wind deflection.
     Maybe in the advanced version let them spring back less than zero with an
initial absence of wind, with some sort of rapid decay back to zero.
Introduce a random rotation or sideways bend, in the event you'll at some point
animate this.

Very nice so far.  I haven't yet tried my hand with any of the plant macros or
plotting a gazillion objects.
(I'll post my tc-rtc WIP on TINA-CHeP soon...)


>What I did is:
>
> 1) Make an image_map with a more or less turbulent ripple pattern.
> 2) Make a height_field based on that image_map.
> 3) Build a reed stalk with Inverse Kinematic properties (macro with Bend
> parameter).
> 4) Select random locations on the height_field;
See above.

> 4a) calculate the vertical angle between the normal at that location and
> a horizontal plane (using: VAngleD(V1,V2));
Use the magnitude of the ripple pattern to directly increase the BEND

> 4b) calculate the horizontal angle between (arbitrarily) the +z-axis
> direction (direction of primary bending of the reed stalks) and the
> normal of the random location point (using: VRotationD(V1,V2,axis)).
Use some arbitrarily determined vector as your (wind) directional vector.
That way you can have it increase and decrease, and change directions like real
wind does, again with an eye toward possible future animation.

> 5a) bend the stalk with a proportion of the vertical angle (4a);
> 5b) orient the bended stalk by rotating through the horizontal angle (4b);
> 5c) place the reed stalks at the random locations on a flat surface.
>
> The image shows 15000 reed stalks. About 4.5 minutes render time.
>
> suggestions are more than welcome of course.
>
> Thomas

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Thomas de Groot <tho### [at] degrootorg> wrote:
> Well, I am interested in modelling wind patterns over a reed field, or a
> corn field. What I seem to observe are turbulent wave patterns moving
> the stalks back and forward while going over the field.
>
> This is a first approximation. I am not really satisfied yet with the
> pattern. What I did is:
>
> 1) Make an image_map with a more or less turbulent ripple pattern.
> 2) Make a height_field based on that image_map.
> 3) Build a reed stalk with Inverse Kinematic properties (macro with Bend
> parameter).
> 4) Select random locations on the height_field;
> 4a) calculate the vertical angle between the normal at that location and
> a horizontal plane (using: VAngleD(V1,V2));
> 4b) calculate the horizontal angle between (arbitrarily) the +z-axis
> direction (direction of primary bending of the reed stalks) and the
> normal of the random location point (using: VRotationD(V1,V2,axis)).
> 5a) bend the stalk with a proportion of the vertical angle (4a);
> 5b) orient the bended stalk by rotating through the horizontal angle (4b);
> 5c) place the reed stalks at the random locations on a flat surface.
>
> The image shows 15000 reed stalks. About 4.5 minutes render time.
>
> suggestions are more than welcome of course.
>
> Thomas

Unfortunatelly I'm not familiar with the macros you use. But your stalks seems
to form a parting, like with hair, close to the right third. The most stalks to
the left of this point are bended to the left the others to the right. So I
wonder about the direction of the wind. I would propose a more simple approach
here. Bend them all in the same direction (with a slight random deviation, due
to the differences in the individual strenght of the stalks). May be you can
model the ground level too, having deeper stalks more straight and bend higher
ones more since they are more influenced by the wind.

Only some short thoughts about the matter,
Best regards,
Micahel

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Am 16.09.2014 16:24, schrieb Thomas de Groot:
> Well, I am interested in modelling wind patterns over a reed field, or a
> corn field. What I seem to observe are turbulent wave patterns moving
> the stalks back and forward while going over the field.

Looks quite promising for a start.

> suggestions are more than welcome of course.

Sure.

It seems to me that you're bending any given reed with a constant radius 
along the whole length of the stalk; I suspect that the stalk should 
bend most strongly at the base, because of (a) the wind acting not only 
on the tip of the stalk, but also on lower portions, so that the wind 
force affecting the bending of any given point increases downward along 
the stalk, (b) the stalk acting as a lever, further amplifying the 
bending force exerted on any given point on the stalk based on how far 
it is from the tip, and (c) the wind force acting upon a near-vertical 
portion of the stalk being stronger than that acting upon a 
near-horizontal portion.

The reeds should bend in a single direction only (albeit at different 
amplitudes) - the primary direction of the wind.

As for the waves, I guess they are not from turbulences already present 
in the wind, but rather from upright reeds "shadowing" those further 
downwind causing them to rise again, while themselves being exposed to 
the wind and beginning to move downward; this effect might be initiated 
and amplified by the individual reeds also resonating in the wind due to 
(c).

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Le 14-09-16 14:39, clipka a écrit :
> Am 16.09.2014 16:24, schrieb Thomas de Groot:
>> Well, I am interested in modelling wind patterns over a reed field, or a
>> corn field. What I seem to observe are turbulent wave patterns moving
>> the stalks back and forward while going over the field.
>
> Looks quite promising for a start.
>
>> suggestions are more than welcome of course.
>
> Sure.
>
> It seems to me that you're bending any given reed with a constant radius
> along the whole length of the stalk; I suspect that the stalk should
> bend most strongly at the base, because of (a) the wind acting not only
> on the tip of the stalk, but also on lower portions, so that the wind
> force affecting the bending of any given point increases downward along
> the stalk, (b) the stalk acting as a lever, further amplifying the
> bending force exerted on any given point on the stalk based on how far
> it is from the tip, and (c) the wind force acting upon a near-vertical
> portion of the stalk being stronger than that acting upon a
> near-horizontal portion.
>
> The reeds should bend in a single direction only (albeit at different
> amplitudes) - the primary direction of the wind.
>
> As for the waves, I guess they are not from turbulences already present
> in the wind, but rather from upright reeds "shadowing" those further
> downwind causing them to rise again, while themselves being exposed to
> the wind and beginning to move downward; this effect might be initiated
> and amplified by the individual reeds also resonating in the wind due to
> (c).
>

In a field, the wind can't affect the stalks near the base because the 
other stalks up wind will shield those downwind. So, the wind only 
affect the top part as soon as you are a few meters from the wind facing 
edge.

The stalks tend to be slightly broader near the base, making them stiffer.

In most cases, there is some sort of flowering or grapes of seeds near 
the top, increasing the surface exposed to wind and adding some height 
neat the tips.

This combine in making the stalks bend in a smooth way with the maximum 
curvature somewhere near mid height.



Alain

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> I suspect that the stalk should
> bend most strongly at the base, because of (a) the wind acting not only
> on the tip of the stalk, but also on lower portions, so that the wind
> force affecting the bending of any given point increases downward along
> the stalk,

I would say that it decreases as you approach the ground.  See Alain's comments,
although I would say that the maximum force/curvature would be near the top.
There is the shielding effect, the tapering effect, the higher surface area due
to flowering, and also the laminar flow issues.

> (b) the stalk acting as a lever, further amplifying the
> bending force exerted on any given point on the stalk based on how far
> it is from the tip

True, but it's all to easy to "reason in reverse" and come up with exactly the
opposite conclusion.   Can't tell you how many times I've done that.  :\

>(c) the wind force acting upon a near-vertical
> portion of the stalk being stronger than that acting upon a
> near-horizontal portion.

?  Not sure what you meant by that.

>
> The reeds should bend in a single direction only (albeit at different
> amplitudes) - the primary direction of the wind.

True, but often there is some asymmetry to the stalk - they might be elliptic in
cross-section, and sometimes IIRC they are almost tear-shaped, with a thin rigid
rib at the thinnest portion.  Depending upon the orientation of that and the
direction of the wind, that could give rise to a twisting effect.
I suppose searching for some IRL video would be in order.

> As for the waves, I guess they are not from turbulences already present
> in the wind, but rather from upright reeds "shadowing" those further
> downwind causing them to rise again, while themselves being exposed to
> the wind and beginning to move downward; this effect might be initiated
> and amplified by the individual reeds also resonating in the wind due to
> (c).

I'm not quite sure exactly what the waves are a result of, but anyone who's done
and has studied long-range ballistics knows that wind speed and direction can be
all over the place between you and what you're looking at 400 yards away.
What's going on where you are, what's going on at where you're looking, and
what's going on at various places in between can vary and even be in complete
opposition.
Consider a tornado, where on one side the air is moving North, and on the other
side it's moving South.  Ditto East & West.
The same kind of thing can happen in vertical strata as well.

I think Thomas needs funding to study the issue....    ;)

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That back bending is simply unrealistic. Just changing the bending 
direction already improves things. What I did was add 180 degrees to all 
negative rotations.

Thanks for all the suggestions.

@ Bald Eagle: I do indeed use the image_map as a kind of force map, 
through the height_field stage and then using the properties of the 
normals. Basically, I think that is identical to what you suggest? The 
rate of bending is proportional to the normal: pointing upward => no 
bending; increased bending with increasing normal angle towards the 
horizontal.

@ MichaelJF: Yes, that parting was killing the effect and came from my 
concept of rebounding of the stalks. In any case, this was far to strong 
here. I presently dropped this effect for the time being.

@ clipka: the bending angle is uniform over the whole length as a first 
approximation. In reality, I expect bending to increase towards the top, 
due to the different effects already mentioned by Alain and Bald Eagle. 
Most important in my view are the thickness/rigidity of the stalks 
towards the base and the damping effect of surrounding stalks. The 
former is easy to implement, the latter is more difficult, especially if 
one also wants to consider collision effects. At present, I do not know 
how to tread that path.

Something I still believe not right is the wave length of the effect. I 
think it should be larger.

Also note in the present image that all stalks start from the same 
initial orientation/scale. I need to introduce more randomness /and/ add 
different types of stalks.

Thomas

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Thomas de Groot wrote on 16/09/2014 16.24:
> Well, I am interested in modelling wind patterns over a reed field, or a
> corn field. What I seem to observe are turbulent wave patterns moving
> the stalks back and forward while going over the field.
>

It looks promising and somehow organic (why it remembers me the seaweed 
salad?).
A nice technique,
;-)
Paolo

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Thanks Paolo.

As a bonus, this image with randomisation of scale and initial vertical 
rotation. Also, bending diminishes downwards.

Thomas

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Am 17.09.2014 13:30, schrieb Thomas de Groot:
> Thanks Paolo.
>
> As a bonus, this image with randomisation of scale and initial vertical
> rotation. Also, bending diminishes downwards.

I concede that it looks good this way.

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