irfpy.cy1orb.pvat2

Spacecraft position and attitude

The module irfpy.cy1orb.pvat2 provides functionality of - Spacecraft position

  • Position in LSE frame

  • Position in ME frame

  • Spacecraft attitude - Convert between LSE frame and spacecraft (SC) frame

For frame conversions, please refer also to How to convert between frames.

Setup

See Position of Chandrayaan-1 for the setup.

Warning

The returned values are in irfpy.util.vector3d, which should be modified in some ways.

Getting position

To get the position of spacecraft, one can use either of the function.

>>> import datetime
>>> from irfpy.cy1orb import pvat2 as pvat
>>> t = datetime.datetime(2009, 5, 10, 3, 10)
>>> pos_lse = pvat.getlsepos(t, asarray=True)
>>> print(pos_lse)
[1396.34 1005.16  633.71]

>>> pos_me_lonlatalt = pvat.getmepos(t)
>>> print(pos_me_lonlatalt)    # The returned value is longitude, latitude and altitude
(28.6, 21.2, 96.1)

>>> pos_me_xyz = pvat.getmepos(t, asarray=True)
>>> print(pos_me_xyz)
[1501.32901199  818.5511499   663.25562399]

Conversion between LSE and SC

The spacecraft frame and LSE frame conversion can be doen using - lse2sc(), from LSE to SC - sc2lse(), from SC to LSE

The example below will give the representation of the spacecraft x-axis in the LSE frame.

>>> vec = sc2lse(datetime.datetime(2009,1,25,14,0,0), [1, 0, 0])
>>> print(vec)
[-0.8204  0.5718 -0.0042]

The next example will give the representations of LSE x-axis in the SC frame. Since LSE a-axis is toward the Sun, the returned vector is the Sun direction in the SC frame.

>>> vec = lse2sc(datetime.datetime(2009,1,25,14,0,0), [1, 0, 0])
>>> print(vec)
[-0.8204      0.0147      0.57163338]

To convert the LSE frame to ME (lunar fixed) frame, see the module irfpy.cy1orb.lseme.

irfpy.cy1orb.pvat2.clear_cache()[source]

Clear the cache.

Usually user do not need to use this function.

irfpy.cy1orb.pvat2.getlsepos(t, asarray=False)[source]

Get LSE orbit at the time of t.

The LSE postiion of Chandrayaan-1. The unit is km.

The returned position of the spacecraft is at the sampling time (1 sec resolution) closest to the specified time.

Parameters

  • t – Time of the data to inquire

  • asarray – If True, numpy array is returned. Otherwise, Vector3d is used.

Returns

The position of spacecraft.

Return type

Vector3d (default) or np.narray (as_array=True)

irfpy.cy1orb.pvat2.getsza(t)[source]

Get the solar zenith angle at the specfied time.

irfpy.cy1orb.pvat2.getmepos(t, as_vector=None, asarray=False, asvector=False)[source]

Get s/c position in ME frame as an array of [lon,lat,height].

lon and lat is in degrees, height is in km above the surface.

>>> me=getmepos(datetime.datetime(2009,4,18,1,30,0))
Param

Time to inquire

Parameters

  • as_vector – Deprecated. Same effect as asarray

  • asarray – Return as numpy array, in km.

  • asvector – Return as Vector3d class object.

Returns

The position of the spacecraft. Default is (longitude, latitude, and height). Angles in degrees, and height in km. If asarray is True, the returned is [x, y, z] in the ME frame in km. If asvector is True, the returns is Vector3d(x, y, z).

irfpy.cy1orb.pvat2.getlsevec(t, vec_in_sc)[source]

Convert the SC -> LSE.

Get LSE-frame vector correspoinding to the SC-frame vector at the time of t. The returned variable is vector3d.Vector3d instance.

>>> vec = getlsevec(datetime.datetime(2009,1,25,14,0,0),
...            vector3d.Vector3d(1, 0, 0))
>>> print(vec.x, vec.y, vec.z)
-0.8204 0.5718 -0.0042
irfpy.cy1orb.pvat2.sc2lse(t, arr_sc)[source]

Convert SC -> LSE

Get LSE-frame arrray correspoinding to the given SC-frame array at the time of t.

Parameters

  • t – Time

  • arr_sc – (…, 3) shaped array in SC frame

Returns

(…, 3) shaped array in LSE frame

>>> vec = sc2lse(datetime.datetime(2009,1,25,14,0,0),
...            [1, 0, 0])
>>> print(vec)
[-0.8204  0.5718 -0.0042]

>>> arr_sc = [[1, 0, 0], [0, 1, 0]]
>>> arr_lse = sc2lse(datetime.datetime(2009,1,25,14,0,0), arr_sc)
>>> print(arr_lse)
[[-0.8204  0.5718 -0.0042]
 [ 0.0147  0.0284  0.9995]]
irfpy.cy1orb.pvat2.get_sc2lse_matrix(t)[source]
irfpy.cy1orb.pvat2.getscvec(t, vec_in_lse)[source]

Convert LSE -> SC.

Inverse function of getlsevec().

Conversion from LSE vector to SC vector at the time of t. The returned is vector3d.Vector3d instance.

>>> vec = getscvec(datetime.datetime(2009, 1, 25, 14, 0, 0),
...             vector3d.Vector3d(1, 0, 0))
>>> print('{:.4f} {:.4f} {:.4f}'.format(vec.x, vec.y, vec.z))
-0.8204 0.0147 0.5716
irfpy.cy1orb.pvat2.lse2sc(t, arr_lse)[source]

Convert LSE -> SC.

Inverse function of sc2lse().

Conversion from LSE vector to SC vector at the time of t.

Parameters

  • t – Time

  • arr_sc – (…, 3) shaped array in SC frame

Returns

(…, 3) shaped array in LSE frame

>>> vec_sc = lse2sc(datetime.datetime(2009, 1, 25, 14, 0, 0), [1, 0, 0])
>>> print('{v[0]:.4f} {v[1]:.4f} {v[2]:.4f}'.format(v=vec_sc))
-0.8204 0.0147 0.5716
irfpy.cy1orb.pvat2.get_lse2sc_matrix(t)[source]
irfpy.cy1orb.pvat2.getdatarange()[source]

Return the data range.

Returns

The range of the data that can be accessed.

Return type

util:irfpy.util.timeinterval.timeinterval instance.

>>> trange = getdatarange()
>>> print(datetime.datetime(2009, 3, 1, 0) in trange)
True
>>> print(datetime.datetime(2008, 12, 8, 0) in trange)
False
>>> print(datetime.datetime(2009, 9, 1, 0) in trange)
False