You can use DI to find a pile in front of you as well. If you don't see it on 2d, you can turn the trolling motor side to side and watch for the pile or school to appear. If you know it is in front of you, and you know the beam goes out perpendicular to the direction of your trolling motor arrow, you know when you see it appear that you need to cast 90 degrees to the direction of the trolling motor arrow.