Gnomonic projection (deg).

def gnomonicSphereToImage(lon, lat):
    """
    Gnomonic projection (deg).
    """
    # Convert angle to [-180, 180] interval
    lon = lon - 360.*(lon>180)
    lon = np.radians(lon)
    lat = np.radians(lat)
    r_theta = (180. / np.pi) / np.tan(lat)
    x = r_theta * np.cos(lon)
    y = r_theta * np.sin(lon)
    return x, y