r.RayTracing.Geometry.Landscape.FractionalLODUpdateThreshold

Minimal difference in fractional LOD between latest built/cached ray tracing geometry and latest value used for rendering (default 0) 0.1 implies a 10% change in the fraction LOD, for instance a change from LOD level 1.1 to 1.2 Larger values will reduce the number of landscape tile updates, but introduce more error between the ray tracing and raster representations