Subdirectories contain all the lightcurves in ZTF DR6 in Parquet format,
grouped by field id.

Details on file content and format are documented in:
https://www.ztf.caltech.edu/page/dr6#12c

See also these Parquet references:
https://pandas.pydata.org/docs/user_guide/io.html?highlight=parquet#io-parquet 
https://arrow.apache.org/docs/python/parquet.html
https://parquet.apache.org/

There are 1105 field subdirectories, containing a total of 150,892 
Parquet files, one for each field/chip/quadrant/filter combination.

A list of corresponding MD5 checksums is also provided.
On a Unix/Linux OS, the files can be verified using 
"md5sum -c checksum.md5".

Total volume: ~ 3.5 TB.

Lightcurve statistics in g-filter:
Number of lightcurves with >= 1  epoch : 1,257,599,606
Number of lightcurves with >= 2  epochs: 1,034,538,802
Number of lightcurves with >= 5  epochs:   865,765,202
Number of lightcurves with >= 10 epochs:   756,050,601
Number of lightcurves with >= 20 epochs:   625,908,286

Lightcurve statistics in r-filter:
Number of lightcurves with >= 1  epoch : 2,042,798,501
Number of lightcurves with >= 2  epochs: 1,747,084,978
Number of lightcurves with >= 5  epochs: 1,494,909,650
Number of lightcurves with >= 10 epochs: 1,337,139,908
Number of lightcurves with >= 20 epochs: 1,168,606,458

Lightcurve statistics in i-filter:
Number of lightcurves with >= 1  epoch :   364,793,132
Number of lightcurves with >= 2  epochs:   238,740,994
Number of lightcurves with >= 5  epochs:   149,732,359
Number of lightcurves with >= 10 epochs:   112,107,375
Number of lightcurves with >= 20 epochs:    82,569,936

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Last modified: 2021 June 22