grass displacement issue (mental ray)

[3d-Soul]

Hi,

I'm doing some test renders from my current project and have a vexing issue with my grass material.
please see the attachment, I really can't understand why these weird shapes appear over my grass objects.
it seems (I'm not sure) that those are view-dependent.

any suggestion is welcome..

[Anonymous]

I've encountered the same problem .. do you have any solution ..

[PROH]

Hi. It looks like you haven't assigned any smoothing groups to the grass areas. Select all your grass areas, assign the same smoothing group to them all and see if the problem is gone.

Hope it helps.

[Anonymous]

You've got them everywhere, even in the front area of grass, but it's less noticeable 😉

I would try to subdivide the displaced surface to get more polygons.

Maybe it help with addition of smoothing group - as PROH mentioned.

[Anonymous]

The problem lies in the fact that your geometry has irregularly shaped polygons. They should be in a grid of evenly sized quads for displacement to give correct results.

So why does this occur you might ask? When displacement is calculated each polygon gets subdivided X amount of times.

If 1 polygon has a larger surface area than the polygon next to it, the displacement subdivisions wil be larger and will therefore look different than the polygon next to it. (See attached images)

Instead of remodeling the mesh from scratch to quads, check out Populate:Terrain first, it's a free terrain remeshing plugin.

It might get you the result you need without all the manual labour. 🙂

Hope that helped!

M.