Vray dirt only in world Z

[pailhead]

I'm trying to figure out if it's possible to use vray dirt in just one direction. I understood that bias controls could be used for this purpose but i don't really understand how they work, because i'm not seeing much difference no matter how high values i'm using for bias.


For example if i have a balcony on a flat facade, can i simulate dirt just under the balcony, not on it's sides?

How does bias work. If i set negative values for Z will it squeeze the dirt in Z direction compared to the x and y?

[DrJan]

First tip: Get the VRay: The Complete Guide book ^^

Second: Setting Z-bias too 100 will make the dirt go down only (instead of both up and down)
You will keep the X and Y dirt though. I have no tried this myself.

[peterguthrie]

Hi Pailhead,

Try setting the distribution to something higher than 1, (10 seems to work well in a very simple test) and the falloff to 1, and then the z bias to 1. As you say, changing the x and y bias seems to mess up the downwards effect..

On jpg attached the one on the left has the settings above, the one on the right has distribution and falloff both at 0.

EDIT: Values greater than 1 for the bias dont seem to make any difference.

Peter