[Spoilers] How did Madara/Obito know the HQ position?

[goodguyjoseph]

Considering the wide range of the shot by the juubi, maybe even without the exact location, just an approximation or some sort, plus the ability of the zetsus, or maybe reversing like the black rods just like Naruto did, there could be many ways to know the location of the HQ, especially for Madara.