Displacement errors

[Shimakaze]

I've been testing out displacement for grass and have run into some unexpected problems. If you look at the attached pictures, for some reason a strange pattern appears. As the ground is made from a plane object it's all quads, and the displacement map is a noise map. I've tried all sorts of settings with both 3d and 3d displacement and I keep getting the same problem. At first I thought it was some sort of moire effect but that doesn't appear to be the case.
Any ideas?

[vlado]

You have correctly guessed that it is a sampling issue where your displacement map has more detail that captured by the displacement.

If you are using 2d displacement, this can be reduced by increasing the sampling "Resolution" parameter. This will take more memory though.

If you are using 3d displacement, you can reduce the Edge length, although this will use additional memory and may slow down the rendering.

In general for such shots where the grass detail is too small to be noticed, it may be better to use a bump map instead.

Best regards,
Vlado

[Morbid Angel]

I may also add that this issue is not vray bound. Mental ray has the same problem. Indeed the 2d map will be a good solution. With 3d displacement the edge length will have to be so low, that the render times are going to be unacceptable.

[Shimakaze]

Thank you for the info. I managed to find a trade-off where it looked good while hiding the artifacts by the textures. I will have to mix different techniques for different distances in the future though I suppose.