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Opt in to flat geometry under AltitudeMode.RELATIVE_TO_GROUND: vertex altitudes anchor to a single terrain sample at the polygon's reference position. Default false keeps per-vertex draping (KML 2.x semantics). Set true for a fixed-AGL surface or a floating extruded slab (non-zero baseAltitude without a ground-anchored foundation); on extruded shapes it flattens the skirt too.