View Full Version : gradient for velocity for particles, wind in atmosphere

03-12-2007, 05:55 PM
yes, i searched the forum, albeit briefly...so i hope this isn't a duplicate.

here is the basis of the situation.

1) the atmosphere is windy
2) the wind in the atmosphere primariy is a function of altitude, generally getting windy-er with altitude and sometimes changing direction.
3) i know that i can use the "motion" tab of the "FX_Emitter" setup window to give a velocity to a particle based on it's altitude above ground.

here is the specific problem:
4) i can't rely on that motion tab of fx emitter because i'm using the velocities there to control velocity of the particle as it is emitted from it's parent.
5) i would like to be able to vary wind in the XZ plane as well, not just with altitude
6) using various "wind emitter" objects scaled and distributed around my scene is a POSSIBLE work around, but not as scientific as i would like, as the falloff within each wind object boundary is somewhat arbitrary

so does anyone understand what i'm trying to ask here? it's the end of the day, so excuse any confusion i may have caused. my ideal plug-in would be capable of creating a global wind that varies with altitude and with X-Z position from the zero point. realize that there is nothing symmetrical about the problem, i.e. a gradient with "distance from object" for X, Y and Z would create an effect, but a symmetrical effect, an i need further control over the wind.

thanks for your help

03-12-2007, 06:06 PM
Add a wind emitter and turn fall off OFF. Set the vector to be 1,0,0 or an equivalent direction. In the POWER field, add a texture and make it a gradient with Input set to Y distance to Object then choose an object which is at ground level. Set your gradient keys to whatever strength you want the wind.

Add other wind emitters to mix up the motion, with their Blend modes set to Add. You can also layer more textures on top of the gradient to give you more control.

Here's an example scene.

03-13-2007, 10:55 AM
you know, i tried that Y distance to object trick, and it didn't seem to work at first, i was guessing that it was adjusting the wind based on the Y distance from the "wind emitter object" to the "reference object" and not within the dimension of the wind emitter itself. i'll go back and try this technique again. i tried to open you scene, it said newer version required. i'm running 9.0 on Mac.


03-13-2007, 11:03 AM
Ah sorry, I'm fully committed to 9.2 :)

03-13-2007, 11:10 AM

you forced me to try again and indeed the gradient works. i think i had something wrong before in my gradient parameters (late-afternoon-brain-fade). i will be using a gradient layer based on "y distance to object" for both wind strength and wind direction. these textured layer gradients are very powerful.

hard to believe 9.0 wouldn't open 9.2...suppose i need to download a patch.

thanks for your vaulable time to help me.


03-13-2007, 11:28 AM
uh oh, should have tried this before my last post. here is the problem now, the changing speed with altitude works great but not direction.

when i apply a texture to the wind vector, it applies the same texture map to all three directions X Y Z. in other words, i could not change direction with altitude without blending other wind objects, which i guess is acceptable...

AH HA! a eureka....

i will model the atmosphere with 3 wind objects:

and change their strength with altitude using a gradient "y distance to object". although homogenous, i can now create an atmosphere that has a wind direction and speed exactly as desired. a nifty microsoft excel document will help me calculate the spline shape for each component of the vector.

hope this helps someone in the future!