For 3D rendering purposes and minimizing .stl file size,  I need to generate an object with different values of PlotPoints and MaxRecursion for different parts of its geometry.  For example, I want to define a shelled sphere with a groove cut out of it.  The inside and outside surfaces of the sphere can be low resolution (Plotpoints -> low , MaxRecursion -> low ), but the equation-driven groove needs to be high resolution.  This cannot be achieved in a single RegionPlot3D[.....] command, so I tried using "Show", and excluding the groove region from the shell region using "not", but it doesn't work:Any ideas?