healpy.rotator.rotate_alm

healpy.rotator.rotate_alm(alm, psi=0.0, theta=0.0, phi=0.0, matrix=None, lmax=None, mmax=None)

This routine transforms the scalar (and tensor) a_lm coefficients to emulate the effect of an arbitrary rotation of the underlying map. The rotation is done directly on the a_lm using the Wigner rotation matrices, computed by recursion. To rotate the a_lm for l ≤ l_max the number of operations scales like l_max^3.

Parameters:

almarray-like of shape (n,) or (k,n), or list of arrays

Complex a_lm values before and after rotation of the coordinate system.

psifloat

First rotation: angle ψ about the z-axis. All angles are in radians and should lie in [-2pi,2pi], the rotations are active and the referential system is assumed to be right handed. The routine coordsys2euler zyz can be used to generate the Euler angles ψ, θ, φ for rotation between standard astronomical coordinate systems.

thetafloat

Second rotation: angle θ about the original (unrotated) y-axis

phifloat.

Third rotation: angle φ about the original (unrotated) z-axis.

matrixnp.ndarray

Rotation matrix instead of angles, for example the output of hp.Rotator.mat

lmaxint

Maximum multipole order l of the data set.

mmaxint

Maximum degree m of data set.