Some suggestions for improving the SLRdata package

[lcx366]

The SLRdata package undoubtedly provides great convenience for generating the CPF prediction and reading the SLR data in CRD format. However, it will be better if (1) add a method to show the avaliable prediction range in time, such as my_predict.info(); enable to set the start and end times as well as the step size (for example, 1 minute) and output the prediction to a file. (2) enable to add the coordinates(lat, lon, height) of a site, and consider the leap second and a prior time bias (3) enable to output the MJD, Seconds of Day, azimuth, elevation, range to the target and 2-way flight time besides cartesian coordinats of the target w.r.t. the geocenter. Hope to make some improvements to make it powerful.

[dronir]

Hey, thanks for the comment. I wrote this originally just for some internal use and didn't have time to more fully develop it beyond the basic functionality I needed then. I'll try to give it a bit more time this summer as one of our students might be needing it, but I can't guarantee continued attention.

[lcx366]

Thanks for your effort on this work. Another issue is about the parse_CRD. After reading the file “ajisai_20190616.npt”(from CDDIS) with parse_CRD, the Units[1]['sessions'][0] gives

{'data': array([], dtype=float64),
 'start': datetime.datetime(2019, 6, 14, 19, 25, 51),
 'end': datetime.datetime(2019, 6, 14, 19, 29, 41),
 'troposphere_corrected': 0,
 'CoM_corrected': 0,
 'receive_amplitude_corrected': 0,
 'station_delay_corrected': 1,
 'spacecraft_delay_corrected': 0,
 'range_type': 2,
 'data_quality': 0}

and the 'data' is an empty array. Trying to read the file “lageos1_20190616.npt” with parse_CRD, it gives

---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-99-a2ad3cd7d60f> in <module>
----> 1 Units = parse_CRD(raw_data)

~/anaconda3/envs/py36/lib/python3.6/site-packages/SLRdata-0.2-py3.6.egg/SLRdata/parse_crd.py in parse_CRD(data)
    111         if line.startswith("H4"):
    112             # Start of session, add new session to active unit.
--> 113             active_session = parse_session(line)
    114             active_unit["sessions"].append(active_session)
    115         if line.startswith("H8"):

~/anaconda3/envs/py36/lib/python3.6/site-packages/SLRdata-0.2-py3.6.egg/SLRdata/parse_crd.py in parse_session(line)
     58             hour = int(line[37:39]),
     59             minute = int(line[40:42]),
---> 60             second = int(line[43:45])
     61         ),
     62         "troposphere_corrected" :  int(line[49]),

ValueError: year -1 is out of range

Maybe the parse_CRD needs to make some adjustments. Anyway, thank you for sharing.

[dronir]

The first problem is because the code is simply not able to read normal points: I wrote it to read raw ranging data so it has no parser to handle lines with normal point data, therefore the data is empty. I guess this is something I should implement soon…

That second error seems like a problem with the data file. The file has a line:
h4 1 2019 6 16 7 51 10 -1 -1 -1 -1 -1 -1 0 0 0 0 1 0 2 0
where the end timestamp of the session is all -1, which can't be parsed into a datetime object.

[dronir]

Ok, setting the timestamp to -1 is part of the CRD specification and should be interpreted as some kind of "N/A". I'll have to handle that, too.

[dronir]

A year later, but got around to looking at this code again since I'm looking at some SLR data again. It should handle normal points now (with not much finesse but still). Haven't fixed the date issue yet, though.

[dronir]

There is also now a method called write_data on the CPF structure, that will dump the raw prediction data as a (N,4) shaped table of timestamps and X, Y, Z, into a file using a column separator given by a user (or defaulting to comma).

[dronir]

Now the ranging data should handle the unspecified timestamps, too. They will be None.

I also added a function to dump the ranging data in CSV too. This is a function in the module called dump_unit(unit, filename, delim=",") and it takes one "unit" from a CRD file and writes it with the given delimiter.

[lcx366]

Nice job. Recently, I also wrote a Python package, slrfield, which is under construction. At present, it can implement the download of CPF ephemeris and make predictions of satellites relative to a specific station. In addition, it can also pick out targets from the DISCOS and CELESTRAK database according to the shape, size, orbit parameters, etc.; and calculate one-day transit passes and multiple-day visible passes for these targets.