Only interested in using a grayscale map to displace a layer in true 3D?

3D Displacer brings true three dimensional displacement mapping to After Effects.  Displacement maps can of course be animated, adding effects like rippling water or blowing flags in full 3D perspective - no faking.  Use mesh subdivision to raise and lower the density of your mesh , and anti-aliasing settings to work quickly and then switch to a fully refined result.