# I control the direction of the wind field with the direction of an object

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Hi,

I'm pretty new to houdini so probably this is very basic.

How can I control the direction of the wind field with the direction of an object?

I hope someone can help

Tks!

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Get the Object Centroid. Get the velocity of that point.

Now in the Wind Field DOP, under the direction parameters, read the velocity using a point expression for each of the respective axis. You can multiply that value by -1, if you want the Wind blowing in the opposite direction.

Edited by bloodhawk
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Tks, but I'm not sure I can do all that. I'm missing some basics.

Can you upload a simple scene?

Tks!

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Ok I did it. Tks!

But now I'm trying something a bit different.

Now I would like to find the velocity of the faces of a rotating object. Then This object will be a volume that will control the amount of wind on a grass field, this part is working, I just need to be able to transfer the velocity vector of the poly faces to the wind direction.

I think I'm almost there.

I've attached a simple scene

ObjectVelocity.hipnc

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Something like this?

H16.0.550 Indie - ObjectVelocity_v2.zip

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Really cool, I still have soooo much to learn.... tks!

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How can I pass that v value to a DOP's network wind velocity?

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Im attaching my file.

I want to use that object to control the wind force on a field of grass. A part of it it's working. I can affect the hair using the volume of the object and with your help I can get the vel.

But I don't know how to pass that value, per point, to the Wind Velocity. CHOPS might be the solution, I've watched and read loads of stuff by now but I still can't figure it out.

WindDirection.hipnc

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You can use a Sop Solver DOP to set forces for your points.

H16.0.550 Indie - WindDirection_v2.zip

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Cool, so you replaced the DOP net that I had in the file?

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I really appreciate your help, I'm studying what you did and most of it makes sense. Would be hard to get there alone with the knowledge I have now.

Edited by MarioD
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9 hours ago, MarioD said:

Cool, so you replaced the DOP net that I had in the file?

More or less yes, you can still use the same setup inside the Guide Sim DOP instead, just add the multi-solver setup with the sop solver.

Although I honestly haven't used the hair tools in Houdini yet, there might be other methods intended to do the same or similar effect

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Ok so, let me see if I understand. You used a SOP solver so you can use the Geometry (SOP level) to the simulation?

Edited by MarioD
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Yup, something like that. In addition to giving access to all the SOP context nodes, the default nodes (dop import) contains the data of the current sim for you to freely process as you want. In the case of the above example file, I'm simply updating the force. I hope that made sense

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