beamforming target about webrtc-beamforming HOT 1 OPEN

From the code line 43 nonlinear_beamformer.h
SphericalPointf target_direction =
SphericalPointf(static_cast(M_PI) / 2.f, 0.f, 1.f));
We can see the direction seems pi/2, 0, pi. And the center is (0, 0, 0) in self-defined coordinate. Does that mean the 3 radians are the rotation angle with respect to 3 axes (x, y, z) we define before?
However, such (pi/2, 0, pi) rotation doesn't exist, So I guess it should be (pi/2, any, pi), which is the negative Z axis.
Then if we only provide 2 mics with coordinate, seems that we can't determine the Axis, Does it mean: we will have accuracy lower if we only have 2 channels?
By the way, can you provide the coordinate of 3 mics in example: input.wav? Thank you.

from webrtc-beamforming.