Starcraft AI blog

Steamhammer has a scouting feature that works in ZvZ matches: When it sees the position of the enemy’s first overlord, it tries to infer where the enemy base is. See Steamhammer’s new scouting skills. It turned out that on some maps—Icarus and Roadrunner—the inference can be wrong. The reason is that Steamhammer measures the distance from the potential hatchery location, not from the overlord’s start location, which is offset. If 2 bases are at nearly the same distance, the offset can matter.

So I came to the question: At the start of the game, where is zerg’s overlord placed relative to its hatchery?

The answer turned out to be simple. The overlord’s x position is offset by either -99 or +99 from the hatchery, and its y position by either -65 or +65. The position is chosen to be whatever is closer to the center of the map. In code:

overlord.x = hatchery.x + ((hatchery.x < 32 * BWAPI::Broodwar->mapWidth() / 2) ? +99 : -99);
overlord.y = hatchery.y + ((hatchery.y < 32 * BWAPI::Broodwar->mapHeight() / 2) ? +65 : -65);

I don’t promise that this is exactly right. It works in the cases I tested. I imagine that somebody on the OpenBW project could tell us the exact condition.