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sgp4.wrapper.Satrec objects can't be pickled

See original GitHub issue

…but sgp4.model.Satrec objects can:

In [1]: from sgp4.api import Satrec

In [2]: Satrec
Out[2]: sgp4.wrapper.Satrec

In [3]: line1, line2 = (
   ...:   "1 00005U 58002B   00179.78495062  .00000023  00000-0  28098-4 0  4753",
   ...:   "2 00005  34.2682 348.7242 1859667 331.7664  19.3264 10.82419157413667",
   ...: )
   ...: sat = Satrec.twoline2rv(line1, line2)
   ...: 

In [4]: sat
Out[4]: <sgp4.wrapper.Satrec at 0x5649605d0430>

In [5]: import pickle

In [6]: with open("/tmp/save.pkl", "wb") as fp:
   ...:     pickle.dump(sat, fp)
   ...: 
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-6-f3c37eb8fd19> in <module>
      1 with open("/tmp/save.pkl", "wb") as fp:
----> 2     pickle.dump(sat, fp)
      3 

TypeError: cannot pickle 'Satrec' object

In [7]: from sgp4.model import Satrec

In [8]: sat = Satrec.twoline2rv(line1, line2)

In [9]: with open("/tmp/save.pkl", "wb") as fp:
   ...:     pickle.dump(sat, fp)

Issue Analytics

State:
Created 3 years ago
Comments:7 (7 by maintainers)

Top GitHub Comments

1reaction

brandon-rhodescommented, Jan 8, 2021

In summary: the lack of pickling support for sgp4.wrapper.Satrec objects is not affecting me (personally) at the moment, and quite probably adding some boilerplate code using TLEs or OMMs is good enough for serialization.

That’s my guess as well! For the moment, then, I am going to close this, as I don’t ever expect that we’ll add full pickling support for the Satrec C-language objects because of the issues mentioned above. But if you ever find a satellite that won’t correctly round-trip through OMM export and then OMM import, then simply open a new issue describing the problem, and we’ll get it fixed. Thanks!

0reactions

astrojuanlucommented, Jan 8, 2021

Until you commented here I had not considered the idea of using OMMs (or even TLEs) as the serialization format (silly, I know!) but it’s probably the way to go. I found this in https://github.com/satellogic/orbit-predictor/issues/117, but through two very simple __setstate__ and __getstate__ methods I worked around the pickling issue.

…But that was before reading your comment https://github.com/brandon-rhodes/python-sgp4/issues/80#issuecomment-748492738 here, so I’d also like to do some actual benchmarking and see if my solution was good enough or could be improved.

In summary: the lack of pickling support for sgp4.wrapper.Satrec objects is not affecting me (personally) at the moment, and quite probably adding some boilerplate code using TLEs or OMMs is good enough for serialization.

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