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11.4.12. astroML.datasets.fetch_imaging_sample

astroML.datasets.fetch_imaging_sample(data_home=None, download_if_missing=True)

Loader for SDSS Imaging sample data

Parameters :

data_home : optional, default=None

Specify another download and cache folder for the datasets. By default all scikit learn data is stored in ‘~/astroML_data’ subfolders.

download_if_missing : optional, default=True

If False, raise a IOError if the data is not locally available instead of trying to download the data from the source site.

Returns :

data : recarray, shape = (330753,)

record array containing imaging data

Notes

This data was selected from the SDSS database using the following SQL query:

SELECT
  round(p.ra,6) as ra, round(p.dec,6) as dec,
  p.run,                              --- comments are preceded by ---
  round(p.extinction_r,3) as rExtSFD, --- r band extinction from SFD
  round(p.modelMag_u,3) as uRaw,      --- ISM-uncorrected model mags
  round(p.modelMag_g,3) as gRaw,      --- rounding up model magnitudes
  round(p.modelMag_r,3) as rRaw,
  round(p.modelMag_i,3) as iRaw,
  round(p.modelMag_z,3) as zRaw,
  round(p.modelMagErr_u,3) as uErr,   --- errors are important!
  round(p.modelMagErr_g,3) as gErr,
  round(p.modelMagErr_r,3) as rErr,
  round(p.modelMagErr_i,3) as iErr,
  round(p.modelMagErr_z,3) as zErr,
  round(p.psfMag_u,3) as psfRaw,      --- psf magnitudes
  round(p.psfMag_g,3) as psfRaw,
  round(p.psfMag_r,3) as psfRaw,
  round(p.psfMag_i,3) as psfRaw,
  round(p.psfMag_z,3) as psfRaw,
  round(p.psfMagErr_u,3) as psfuErr,
  round(p.psfMagErr_g,3) as psfgErr,
  round(p.psfMagErr_r,3) as psfrErr,
  round(p.psfMagErr_i,3) as psfiErr,
  round(p.psfMagErr_z,3) as psfzErr,
  p.type,                   --- tells if a source is resolved or not
  (case when (p.flags & '16') = 0 then 1 else 0 end) as ISOLATED
INTO mydb.SDSSimagingSample
FROM PhotoTag p
WHERE
    --- 10x2 sq.deg.
  p.ra > 0.0 and p.ra < 10.0 and p.dec > -1 and p.dec < 1
    --- resolved and unresolved sources
  and (p.type = 3 OR p.type = 6) and
    --- '4295229440' is magic code for no
    --- DEBLENDED_AS_MOVING or SATURATED objects
  (p.flags & '4295229440') = 0 and
    --- PRIMARY objects only, which implies
    --- !BRIGHT && (!BLENDED || NODEBLEND || nchild == 0)]
  p.mode = 1 and
    --- adopted faint limit (same as about SDSS limit)
  p.modelMag_r < 22.5
--- the end of query

Examples

>>> from astroML.datasets import fetch_imaging_sample
>>> data = fetch_imaging_sample()
>>> data.shape  # number of objects in dataset
(330753,)
>>> print data.names[:5]  # names of the first five columns
['ra', 'dec', 'run', 'rExtSFD', 'uRaw']
>>> print data['ra'][:2]
[ 0.265165  0.265413]
>>> print data['dec'][:2]
[-0.444861 -0.62201 ]