Shape3D encompass = new Shape3D( geom,  app );
Shape3D decal1    = new Shape3D( geom1, app1 );
Shape3D decal2    = new Shape3D( geom2, app2 );
. . .
DecalGroup decals = new DecalGroup( );
decals.addChild( encompass );
decals.addChild( decal1 );
decals.addChild( decal2 );