What I'd you used this cheap sr04 sensors to find a location in the room ie the middle to make a pile ? That would be pretty simple?
I would imagine you will need to find a way to triangulate your position ... 2 fixed points of ir perhaps such as LEDs ... And a directional sensor ( tube on a receiver ) with angle measurements of some kind?
The better gps units such as gtpa010 are good to a few feet, might work for a leaf pile though?