# How to use mask field node in DOP Network in RBD sim?

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Hi Houdini friends,

Does anyone know how to use mask field in DOP net? I'm doing a simulation of leaves on the ground reacting to a car passing by. I need to control the wind force to affect only where the car is passing, where other leaves remains more still. Is there any way to mask out the affected area and have the wind force only affect that area and have dynamic change on the mask object? Or if there's other ways to do this? Thank you so much!!!

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Cool, that is a nice example file. You can also plug the mask in to gravity, reverse the gravity direction and have particles rise up only when the box passes through them.

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4 hours ago, fencer said:

check

Thanks Fencer! I've checked the file, I'll see if this setup will work in mine too!

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3 hours ago, Atom said:

Cool, that is a nice example file. You can also plug the mask in to gravity, reverse the gravity direction and have particles rise up only when the box passes through them.

Thanks Atom, that's a nice idea!

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On 11/12/2016 at 8:44 AM, fencer said:

check

Hi fencer, I have another problem of this. After the leaves rise up they need to be not affected by the force anymore, but this method it continue to affect the leaves, so they never fall on the ground again. Is there any solution to that? Thanks!!!

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It seems to work for me, there is a gravity force following the wind. You do have to play with the numbers on the Wind Force. This GIF shows the windforce adjusted so the Scale Force is 6, was 60 and the Velocity in the Y-AXIS is 10, was 1. So the overall force is similar, 6 * 10 i.e. 60 but it is split between the input channels in a different way.

Edited by Atom

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33 minutes ago, Atom said:

It seems to work for me, there is a gravity force following the wind. You do have to play with the numbers on the Wind Force. This GIF shows the windforce adjusted so the Scale Force is 6, was 60 and the Velocity in the Y-AXIS is 10, was 1. So the overall force is similar, 6 * 10 i.e. 60 but it is split between the input channels in a different way.

Thanks Atom! I'll try this!

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Hey guys
I'm trying to modify the fencer hip example by adding some noise into the box volume, so what I need is to make kind of noisy shape of the mask to affect the particles

I simply  put volumevop with some noise after the isooffset but all the setup is not working this way, the particles start moving out of the box mask.
Does Sop Scalar Field allows me to do it basically ?

thanks

Edited by JDee

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25 minutes ago, JDee said:

Hey guys
I'm trying to modify the fencer hip example by adding some noise into the box volume, so what I need is to make kind of noisy shape of the mask to affect the particles

I simply  put volumevop with some noise after the isooffset but all the setup is not working this way, the particles start moving out of the box mask.
Does Sop Scalar Field allows me to do it basically ?

thanks

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Still works on 2020 17.5 ;D thanks from the future

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Thanks guys this was really handy, I was also wondering how can we mask forces by other attributes.  Say you wanted gravity only on particles that had reached a certain velocity.

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Is there a way to blur the mask so that it has a soft falloff?

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On 2020-09-10 at 6:52 PM, oaschwab said:

Is there a way to blur the mask so that it has a soft falloff?

Sure, just multiply input volume values. Make gradien 0 to 1.

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