I have noticed that when I extrude a geometry and use elevationInfo as "relative-to-ground" it will follow the elevation only for the points that defines this geometry.
Visually my problem is on the image bellow. The yellow geometry is a ring the is being extruded and it`s border can follow ground elevation, however there is a higher elevation between extremities that is piercing through.
I would like to know if this is a know issue, or if I am missing some configuration for my layer.
I have run into this as well. I think it does not work on the fly with all parts of the polygon. It uses one point and extrudes from there. What I did was broke my polygon into thousands of sections that way it gets extruded properly based on each segment.
We extrude along the edges of the polygon and the interior of the polygon might end up under the terrain in case the terrain is higher in that area. As Rickey suggested, a workaround might be to try and generate multiple polygons and extrude them. So unfortunately, no straight-forward solution as of now.