Drop selection to ground (z=0) in SketchUp

drop to z0

mod = Sketchup.active_model # Open model
ent = mod.entities # All entities in model
sel = mod.selection # Current selection

sel.each { |i|
    vec = Geom::Vector3d.new 0,0,-(i.bounds.min.z)
    t = Geom::Transformation.new vec
    ent.transform_entities(t, i)
}