SPICE aberration corrections

In order to simplify the use of the SPICE aberration corrections, we introduced a SpiceAbCorr object:

from planetary_coverage.spice import SpiceAbCorr

It will check that the provided values are valid:

SpiceAbCorr()

'NONE'

SpiceAbCorr('LT')

'LT'

SpiceAbCorr('XCN+S')

'XCN+S'

SpiceAbCorr('FOO')

---------------------------------------------------------------------------
KeyError                                  Traceback (most recent call last)
Cell In[5], line 1
----> 1 SpiceAbCorr('FOO')

File ~/checkouts/readthedocs.org/user_builds/planetary-coverage/checkouts/stable/src/planetary_coverage/spice/abcorr.py:59, in SpiceAbCorr.__new__(cls, abcorr, restrict)
     56     restrict = cls.DEFAULTS
     58 if abcorr not in restrict:
---> 59     raise KeyError(
     60         f'Invalid abcorr: `{abcorr}`. Available: ' +
     61         '|'.join(restrict)
     62     )
     64 return str.__new__(cls, abcorr)

KeyError: 'Invalid abcorr: `FOO`. Available: NONE|LT|LT+S|CN|CN+S|XLT|XLT+S|XCN|XCN+S'

You can restrict the list of the valid keys if you need to:

SpiceAbCorr('LT', restrict=('LT', 'LT+S'))

'LT'

SpiceAbCorr('CN', restrict=('LT', 'LT+S'))

---------------------------------------------------------------------------
KeyError                                  Traceback (most recent call last)
Cell In[7], line 1
----> 1 SpiceAbCorr('CN', restrict=('LT', 'LT+S'))

File ~/checkouts/readthedocs.org/user_builds/planetary-coverage/checkouts/stable/src/planetary_coverage/spice/abcorr.py:59, in SpiceAbCorr.__new__(cls, abcorr, restrict)
     56     restrict = cls.DEFAULTS
     58 if abcorr not in restrict:
---> 59     raise KeyError(
     60         f'Invalid abcorr: `{abcorr}`. Available: ' +
     61         '|'.join(restrict)
     62     )
     64 return str.__new__(cls, abcorr)

KeyError: 'Invalid abcorr: `CN`. Available: LT|LT+S'

To be fully compatible with spiceypy, it extends directly from the python base class str:

abcorr = SpiceAbCorr('LT+S')

isinstance(abcorr, str)

True

abcorr == 'LT+S'

True

with a few additional properties:

abcorr.reception

True

abcorr.transmission

False

abcorr.stellar

True

abcorr.oneway

True

abcorr.converged

False

Finally, you can apply the light time correction based on the provided key:

et, lt = 10, 2

abcorr = SpiceAbCorr('NONE')
abcorr(et, lt)  # NONE -> et (no correction)

10.0

abcorr = SpiceAbCorr('LT')
abcorr(et, lt)  # LT -> et - lt (reception)

9.999993328718096

abcorr = SpiceAbCorr('XLT')
abcorr(et, lt)  # XLT -> et + lt (transmission)

10.000006671281904