lb_to_tan

ssapy.utils.lb_to_tan(lb, b, mul=None, mub=None, lcen=None, bcen=None)[source][source]

Convert lb-like coordinates & proper motions to orthographic tangent plane.

All units are in radians. If mul is None (default), transformed proper motions will not be returned. The tangent plane is always chosen so that +Y is towards b = 90, and +X is towards +lb.

Parameters:

  • lb (array_like (n)) – right ascension of point

  • b (array_like (n)) – declination of point

  • mul (array_like (n)) – proper motion in ra of point (arbitrary units) rate of change in lb is mul / np.cos(b); i.e., length of proper motion vector on sphere is np.hypot(mul, mub)

  • mub (array_like (n)) – proper motion in dec of point (arbitrary units)

  • lcen (array_like (n)) – right ascension to use for center of tangent plane if None, use spherical mean of (lb, b)

  • bcen (array_like (n)) – declination to use for center of tangent plane

Returns:

  • if mul is None, (x, y) otherwise (x, y, vx, vy)

  • x (array_like (n)) – x coordinate of tangent plane projection of lb, b

  • y (array_like (n)) – y coordinate of tangent plane projection of lb, b

  • vx (array_like (n)) – x coordinate of tangent plane projection of (mul, mub)

  • vy (array_like (n)) – y coordinate of tangent plane projection of (mul, mub)