# irfpy.util.sphere¶

Sphere, a geometry

Bases: object

cut(normal: ndarray, distance: float, resolution: int = 361) list[numpy.ndarray][source]

Get a list of vectors produced by a cut by a plane

Get a set of vectors produced by a cut by a plane, defined by the normal vector and distance from the center.

This method is useful to get vectors that forms

• the equator (distance zero with respective to the pole as normal)

• a latitutde (distance corresponding to the latitude, ie. r sin(lat), with respctive to the pole)

• the terminator (distance 0, w.r.t the subsolar point)

• a solar zenith angle (distance corresponding to the sza, i.e., r cos(sza), w.r.t the subsolar point)

• a longitude (distance 0 w.r.t. a point on the equator 90 degrees off from the latitude)

Parameters:
• normal – The normal vector of the cut plane. (Not necessarily normalized, length does not care).

• distance – The distance from the center. Negative allowed.

• resolution – The resolution.

>>> import numpy as np
>>> sphere = Sphere(1)   # A unit sphere
>>> parallel = sphere.cut([0, 1, 0], 0.5)   # Cut by a xz-plane at y=0.5.
>>> print(len(parallel))   # A list of (3,) ndarray
361

>>> parallel = np.array(parallel)
>>> y = parallel[:, 1]    #  y shall be constant
>>> print(f'{y.min():.2f} {y.max():.2f}')
0.50 0.50

>>> x = parallel[:, 2]    #  x and z should range  sq(0.75)
>>> print(f'{x.min():.3f} {x.max():.3f}')
-0.866 0.866

>>> z = parallel[:, 2]    #  x and z
>>> print(f'{z.min():.3f} {z.max():.3f}')
-0.866 0.866

equator(northpole, resolution=361)[source]
Parameters:

northpole – The north pole direction. (Length doesn’t care)

>>> import numpy as np
>>> sphere = Sphere(1000)
>>> vec = sphere.equator([0, 1, 0])   # If y-axis is the north pole, the the equator is in x-z plane (y=0)
>>> vec = np.array(vec)
>>> vec.shape
(361, 3)
>>> print(f'{vec[:, 1].min():.2f} {vec[:, 1].max():.2f}')
-0.00 0.00
>>> print(f'{vec[:, 0].min():.2f} {vec[:, 0].max():.2f}')
-1000.00 1000.00

latitude(northpole, latitude_deg, resolution=361)[source]

Return the set of vectors, represnting the latitude.

Parameters:
• latitude_deg – Latitude in degrees.

• northpole – North pole coordinates. (Length doesn’t care)

>>> import numpy as np
>>> sphere = Sphere(1000)
>>> vec = np.array(sphere.latitude([0, 1, 0], 30))   # If y-axis is the north pole, the latitude 30 is y=500 km
>>> print(f'{vec[:, 1].min():.2f} {vec[:, 1].max():.2f}')
500.00 500.00

terminator(sun_direction, resolution=361)[source]
Parameters:

sun_direction – Sun direction (from the center), or in other word, subsolar point coordinate. (Length doesn’t care)

>>> import numpy as np
>>> sphere = Sphere(1000)
>>> vec = np.array(sphere.terminator([-0.1, 0, 0]))  # If -x axis is the sundirection, the terminator is x=0.

>>> print(f'{vec[:, 0].min():.2f} {vec[:, 0].max():.2f}')
-0.00 0.00

sza(sun_direction, sza_deg, resolution=361)[source]
Parameters:
• sza_deg – the solar zenith angle.

• sun_direction – The sun direction. (Length doesn’t care)

>>> import numpy as np
>>> sphere = Sphere(1000)
>>> vec = np.array(sphere.sza([0, 0, -2], 60))   # If -z axis is the sun direction, the sza 60 is z=-500 km
>>> print(f'{vec[:, 2].min():.2f} {vec[:, 2].max():.2f}')
-500.00 -500.00