AR is more realistic when virtual objects in your scene cast shadows onto the physical world. 8th Wall XR now provides a shader that can be used on transparent surfaces.
Create a material (for example, call it MyXRTransparentSurface), and select 8thWall -> XRShadow from the list of shaders, then apply the material to the surface object you want to make transparent (i.e. a ground plane):
To adjust the opacity of the shadows, select your Directional Light, and adjust the Strength of the shadow. To improve shadow quality, set resolution to "Very High Resolution"
For improved shadow quality, go to Edit -> Project Settings -> Quality. Set Shadow Resolution to "Very High Quality" and Shadow Projection to "Close Fit"