public boolean actionPlantSensor(Actor actor, Tile t) {
    SensorPost post = null ;
    for (Item i : actor.gear.matches(SAMPLES)) {
      if (i.refers instanceof SensorPost) {
        post = (SensorPost) i.refers ;
        actor.gear.removeItem(i) ;
      }
    }
    if (post == null) return false ;
    post.setPosition(t.x, t.y, world) ;
    if (! Spacing.perimeterFits(post)) return false ;
    post.enterWorld() ;
    return true ;
  }