# Minimum coordinates of all vertices on each axes
	#
	# This is a corner of the bounding box.
	var min: Point3d[Float] is lazy do
		var mx = inf
		var my = inf
		var mz = inf
		for leaf in leaves do
			var lm = leaf.mesh.min
			mx = mx.min(lm.x)
			my = my.min(lm.y)
			mz = mz.min(lm.z)
		end
		return new Point3d[Float](mx, my, mz)
	end