VrayDisplacementMod & Direct Light

[tmccarter]

Hey all,

 

I discovered an interesting behavior exhibited by the VrayDisplacementMod modifier in relation to direct light, and I was wondering if anyone had experienced the same. In the renderings I attached, I have a vray sphere light (size 30', multiplier at 3.5, no decay, ignore light normals checked) and indirect illumination via a HDRI, multplier at 0.5. The light is positioned 850' away and 600' above the subjects, which are a 10' patch of grass plane and some primitives. I'm using vraymtl's for everything. I'm using a grass diffuse map and displacement map from Evermotion's tutorial, which can be found at http://www.evermotion.org/?unfold_exclusive=102&unfold=exclusive. My mod settings are: 2D mapping, amount of 5", shift of '", resolution of 2048, precision of 16. I revolve the light around my subjects, putting the light at different angles (0, 90, 180, 270 shown in my renderings). As I do this, the appearance of the grass dramatically changes. Anybody else experiencing this behavior? Am I setting something incorrectly?

 

Thanks,

 

-Tim

[Crazy Homeless Guy]

i havn't experiemnted extensivly with vray displacement grass, but if you think about your problem, it makes sense. look at the lighting on the box. it very similar to the grass. when the light is directly behind you, shot 3, 3 box is totally washed out, and so is the grass.

 

basically, displacement grass acts as 3d, and will take the same lighting effects as 3d. in the first shot, you are looking at the backside of the 3d grass, so only your GI soluton, and whatever is bounced from your vray sphere will light that side.

 

i can think of 2 things to do about this. first, the blowout on your box. i think you need to down the intensity of the sphere. get it to the point where you box is not blowing out. then look at you grass. it will probably be to dark. so you will need to go back and look at your texture settings for the grass. you can probably adjust them to make the grass appear normal.

 

anyway, maybe those suggestions will help.

 

have you tried to use vray grass in production yet? ...it really screws my rendering times. have you had any luck rendering a full scene in a decent amount of time?

[tmccarter]

Hey crazy homeless,

 

Thanks for the tips. To be honest, we've just learned about this technique so we've only run a few tests on our scene, but it definitely adds a lot of time. Our scene is a residential external with 4 houses and 5 patches of grass. We rendered just the lawns and the sidewalk/street elements, and a 640 x 480 rendering took 15 min on an athlon 64 x2 with 2 gb ram and a quadro fx 3450. I'm scared to see what the times will be with the houses, and trees, and people... yeesh. In any case, I'll keep y'all posted with our progress.

 

Is there another technique for grass that you prefer? So far we really like the results of the vray displacement mod, but I'm always looking for a better way.

 

Anyway, thanks again

 

-Tim

[Crazy Homeless Guy]

not that i know of, 95% of the time i still use a basic texture map on the ground for grass. there is a post about using hair as grass on theboard right now. i have never tried that, so i don't know how the times compare. in theory, hair would be more representative of how grass behaves as a true physical object, so i am guessing the render times with that are not going to be better.

[neba77]

I found out that the quickest way for the grass is using comping techniques. Doing it in scanline, as hair and fur object, with your objects matte-d, and then comping it in photoshop. It takes a while to get a hold of it, but the results can be amasing.