Analyze Dataset

An example on how to use the analyzer to analyze a dataset.

Imports

For this example we will use only xarray and analyze_dataset from enstools-compression.

import xarray
from enstools.compression.analyzer.analyzer import analyze_dataset

WARNING: eccodes c-library not found, grib file support not available!

dataset_name = "air_temperature"
dataset = xarray.tutorial.open_dataset(dataset_name)
dataset

<xarray.Dataset>
Dimensions:  (lat: 25, time: 2920, lon: 53)
Coordinates:
  * lat      (lat) float32 75.0 72.5 70.0 67.5 65.0 ... 25.0 22.5 20.0 17.5 15.0
  * lon      (lon) float32 200.0 202.5 205.0 207.5 ... 322.5 325.0 327.5 330.0
  * time     (time) datetime64[ns] 2013-01-01 ... 2014-12-31T18:00:00
Data variables:
    air      (time, lat, lon) float32 ...
Attributes:
    Conventions:  COARDS
    title:        4x daily NMC reanalysis (1948)
    description:  Data is from NMC initialized reanalysis\n(4x/day).  These a...
    platform:     Model
    references:   http://www.esrl.noaa.gov/psd/data/gridded/data.ncep.reanaly...

xarray.Dataset

• Dimensions:
  • lat: 25
  • time: 2920
  • lon: 53
• Coordinates: (3)
  • lat
    (lat)
    float32
    75.0 72.5 70.0 ... 20.0 17.5 15.0

    standard_name :

    latitude

    long_name :

    Latitude

    units :

    degrees_north

    axis :

    Y

    array([75. , 72.5, 70. , 67.5, 65. , 62.5, 60. , 57.5, 55. , 52.5, 50. , 47.5,
           45. , 42.5, 40. , 37.5, 35. , 32.5, 30. , 27.5, 25. , 22.5, 20. , 17.5,
           15. ], dtype=float32)

  • lon
    (lon)
    float32
    200.0 202.5 205.0 ... 327.5 330.0

    standard_name :

    longitude

    long_name :

    Longitude

    units :

    degrees_east

    axis :

    X

    array([200. , 202.5, 205. , 207.5, 210. , 212.5, 215. , 217.5, 220. , 222.5,
           225. , 227.5, 230. , 232.5, 235. , 237.5, 240. , 242.5, 245. , 247.5,
           250. , 252.5, 255. , 257.5, 260. , 262.5, 265. , 267.5, 270. , 272.5,
           275. , 277.5, 280. , 282.5, 285. , 287.5, 290. , 292.5, 295. , 297.5,
           300. , 302.5, 305. , 307.5, 310. , 312.5, 315. , 317.5, 320. , 322.5,
           325. , 327.5, 330. ], dtype=float32)

  • time
    (time)
    datetime64[ns]
    2013-01-01 ... 2014-12-31T18:00:00

    standard_name :

    time

    long_name :

    Time

    array(['2013-01-01T00:00:00.000000000', '2013-01-01T06:00:00.000000000',
           '2013-01-01T12:00:00.000000000', ..., '2014-12-31T06:00:00.000000000',
           '2014-12-31T12:00:00.000000000', '2014-12-31T18:00:00.000000000'],
          dtype='datetime64[ns]')

• Data variables: (1)
  • air
    (time, lat, lon)
    float32
    ...

    long_name :

    4xDaily Air temperature at sigma level 995

    units :

    degK

    precision :

    2

    GRIB_id :

    11

    GRIB_name :

    TMP

    var_desc :

    Air temperature

    dataset :

    NMC Reanalysis

    level_desc :

    Surface

    statistic :

    Individual Obs

    parent_stat :

    Other

    actual_range :

    [185.16 322.1 ]

    [3869000 values with dtype=float32]

• Indexes: (3)
  • lat
    PandasIndex

    PandasIndex(Index([75.0, 72.5, 70.0, 67.5, 65.0, 62.5, 60.0, 57.5, 55.0, 52.5, 50.0, 47.5,
           45.0, 42.5, 40.0, 37.5, 35.0, 32.5, 30.0, 27.5, 25.0, 22.5, 20.0, 17.5,
           15.0],
          dtype='float32', name='lat'))

  • lon
    PandasIndex

    PandasIndex(Index([200.0, 202.5, 205.0, 207.5, 210.0, 212.5, 215.0, 217.5, 220.0, 222.5,
           225.0, 227.5, 230.0, 232.5, 235.0, 237.5, 240.0, 242.5, 245.0, 247.5,
           250.0, 252.5, 255.0, 257.5, 260.0, 262.5, 265.0, 267.5, 270.0, 272.5,
           275.0, 277.5, 280.0, 282.5, 285.0, 287.5, 290.0, 292.5, 295.0, 297.5,
           300.0, 302.5, 305.0, 307.5, 310.0, 312.5, 315.0, 317.5, 320.0, 322.5,
           325.0, 327.5, 330.0],
          dtype='float32', name='lon'))

  • time
    PandasIndex

    PandasIndex(DatetimeIndex(['2013-01-01 00:00:00', '2013-01-01 06:00:00',
                   '2013-01-01 12:00:00', '2013-01-01 18:00:00',
                   '2013-01-02 00:00:00', '2013-01-02 06:00:00',
                   '2013-01-02 12:00:00', '2013-01-02 18:00:00',
                   '2013-01-03 00:00:00', '2013-01-03 06:00:00',
                   ...
                   '2014-12-29 12:00:00', '2014-12-29 18:00:00',
                   '2014-12-30 00:00:00', '2014-12-30 06:00:00',
                   '2014-12-30 12:00:00', '2014-12-30 18:00:00',
                   '2014-12-31 00:00:00', '2014-12-31 06:00:00',
                   '2014-12-31 12:00:00', '2014-12-31 18:00:00'],
                  dtype='datetime64[ns]', name='time', length=2920, freq=None))

• Attributes: (5)

  Conventions :

  COARDS

  title :

  4x daily NMC reanalysis (1948)

  description :

  Data is from NMC initialized reanalysis (4x/day). These are the 0.9950 sigma level values.

  platform :

  Model

  references :

  http://www.esrl.noaa.gov/psd/data/gridded/data.ncep.reanalysis.html

Analyze dataset using default constrains

Use analyze_dataset to obtain the compression specification that guarantee quality constrains while maximising compression ratios. In this case if the argument constrains is not provided it will use the default ones, which are "correlation_I:5,ssim_I:2".

Note:

correlation_I is computed like: -log10(1-pearson_correlation). i.e. number of nines of correlation

correlation_I:5 == correlation:0.99999

Similarly ssim_I is computed like: -log10(1-ssim).

encoding, metrics = analyze_dataset(dataset=dataset)

WARNING: Only absolute and norm2 modes properly tested
WARNING: Only absolute and norm2 modes properly tested
WARNING: Only absolute and norm2 modes properly tested
WARNING: Only absolute and norm2 modes properly tested
WARNING: Only absolute and norm2 modes properly tested
WARNING: Only absolute and norm2 modes properly tested
WARNING: Only absolute and norm2 modes properly tested
WARNING: Only absolute and norm2 modes properly tested
WARNING: Only absolute and norm2 modes properly tested
WARNING: Only absolute and norm2 modes properly tested
WARNING: Only absolute and norm2 modes properly tested
WARNING: Only absolute and norm2 modes properly tested
WARNING: Only absolute and norm2 modes properly tested

The function returns two dictionaries, one containing the best encoding and another containing the resulting metrics.

encoding

{'air': 'lossy,sz,pw_rel,0.000549'}

metrics

{'air': {'correlation_I': 5.064244624947207,
  'ssim_I': 3.856431344802704,
  'compression_ratio': 7.868889904065783}}

Analyze dataset using custom constrains

If we want to specify different constrains we can do it like this:

encoding, metrics = analyze_dataset(dataset=dataset,constrains="correlation_I:3,ssim_I:1")

WARNING: Only absolute and norm2 modes properly tested
WARNING: Only absolute and norm2 modes properly tested
WARNING: Only absolute and norm2 modes properly tested
WARNING: Only absolute and norm2 modes properly tested
WARNING: Only absolute and norm2 modes properly tested
WARNING: Only absolute and norm2 modes properly tested
WARNING: Only absolute and norm2 modes properly tested
WARNING: Only absolute and norm2 modes properly tested
WARNING: Only absolute and norm2 modes properly tested
WARNING: Only absolute and norm2 modes properly tested
WARNING: Only absolute and norm2 modes properly tested
WARNING: Only absolute and norm2 modes properly tested
WARNING: Only absolute and norm2 modes properly tested