V-Ray rendering tips

Below are some tips, tricks, and recommendations for using Forest Pack with V-Ray

Max Transparency Levels and Transparency Cutoff: When using edge mode or items with lots of transparency leaves, you may need to adjust the Max transparency levels and Transparency Cutoff settings under Global Switches to suit your specific needs.
Avoid Overlapping Geometry: This isn't specific to foliage, but it's good to avoid overlapping geometry. If your model has overlapping elements that you don't wish to adjust manually, you can use the Secondary Ray Bias setting under Global Switches. A value slightly above zero, like 0.001, usually works well.

Disable Filtering on Maps: You might find it beneficial to disable filtering on all maps, whether for opacity or otherwise. This is generally not problematic, especially in still images.
Antialiasing Image Filters: You can also turn off the Antialiasing Image filter options in V-Ray.
Remove Unused Elements: Make sure to remove any unused objects and assets. Include only elements that will actually be visible during rendering.
Blend Materials: While blend materials can add realism, they can also slow down the rendering process. You might want to minimise their use.

Minimise Number of Lights: Using fewer lights can improve render times. If you scatter many lights, be sure to use V-Ray's Adaptive Lights features (these are already enabled by default in latest V-ray releases).

Avoid V-Ray Displacement for terrains covered in scattered objects: This will slow things down and the displacement may interpenetrate the scattered objects. If you don't plan on directly seeing the terrain, instead of V-Ray displacement, subdivide your geometry to an acceptable level and use Max's default Displace modifier.
Polygon Count: Handling fewer objects with more polygons is generally easier on the renderer than the opposite.
Scene Origin: Ensure your scene is not too far from the origin point, especially for models imported from other software like AutoCAD or Revit.
Background Trees: For trees in the background, consider using larger leaves and disabling opacities and 2 sided materials to lower the polygon count. ForestLOD can be used to switch items based on distance from the camera

Ambient Occlusion: If rendering Ambient Occlusion as an additional pass, enable the work with transparency option under VRayDirt Parameters.
High-Density Scatters: In scenes with very high-density scatters like dense grass, you may exceed V-Ray's default transparency limit, causing render artefacts. To mitigate this, either:
1. Reduce density values.
2. Adjust the Max transparency levels under V-Ray render settings. Sometimes it may also be necessary to adjust the Secondary rays bias.