6.2.3 Implicit groundplane

The Implicit Groundplane is a special case of the more general concept of matte objects. It covers the case of a planar surface acting as shadow catcher without the need of an explicit geometry. The Implicit Groundplane works in Iray Photoreal and Iray Interactive.
This implicit ground plane weights the environment contribution of the ground using a progressive estimation of the amount of shadow on the groundplane, caused by the objects in the scene (from direct light only). The mode of the environment lookup itself remains unchanged as it is specified by the environment settings. The groundplane is a special case of the more general concept of matte objects.
Screenshot illustrating the effect of the implicit ground plane. The only polygonal geomety in this scenario is the gargoil character.
Iray Common Implicit Groundplane attributes
Enables the effect of the Implicit Groundplane.
Defines the position of the Implicit Groundplane along the world Y axis.
Shadow Intensity
Defines the darkness of the shadow effect on the Implicit Groundplane.
If set to a positive value, enables reflectivity on the groundplane weighted by the fresnel term.
Controls the glossiness of the ground reflectivity. Useful values range from 0 (diffuse) to 10000000.0 (perfect mirror).
Direct Reflections Only
When set this attribute is enabled, the ground will only reflect objects directly, but not when seen from reflections on other objects. Also, reflections will not replace the (optional) ground shadow, which allows to have highly glossy reflections mixed with diffuse shadowing. For a more physically correct behaviour, turn this attribute off will avoid this, but one has to take care to not mix strong ground shadows with a high ground glossiness (which is equivalent to the behaviour of regular matte objects).
Visible from Below
When this attribute is turned off, one can see geometry located above the ground plane, even when the camera is placed below it.
Connect to Environment
When set to Yes, secondary interactions with the matte object will use the environment instead of the backplate.
Note: Only effective if a backplate function or the backplate color is set.
Connect from Camera
This additional flag makes the matte object behavior toggle between two different lookup types:
Note: The attribute Connect from Camera will only be noticable in scenes where no backplate/color at all is specified (so all interactions will always be happening with the environment), or if a backplate/color is specified and the "Connect to Environment" flag is set in addition.