datasets - Dataset access¶

Introduction¶

gammapy.datasets contains function to easily access datasets that are relevant for gamma-ray astronomy.

The functions have a naming pattern (following scikit-learn lead):

load_* functions load datasets that are distributed with Gammapy (bundled in the repo)
fetch_* functions fetch datasets from the web (either from gammapy-extra repository or other sites)
make_* functions create datasets programatically (sometimes involving a random number generator)

Note

The gammapy.datasets sub-package shouldn’t be confused with the gammapy.data sub-package, which contains classes representing gamma-ray data. And there is a separate section describing the Data Formats that are commonly used in gamma-ray astronomy.

gammapy-extra¶

To keep the Gammapy code repository at https://github.com/gammapy/gammapy small and clean, we are putting sample data files in an extra repository at https://github.com/gammapy/gammapy-extra/ . These sample data files may be fetched with gammapy-download datasets and then point your $GAMMAPY_DATA to the local path you have chosen.

# Download GAMMAPY_DATA
cd code
gammapy download datasets --out GAMMAPY_DATA
export GAMMAPY_DATA=$PWD/GAMMAPY_DATA

Gamma-cat¶

Gamma-cat is an open catalog for TeV gamma-ray sources. It is maintained as an open git repository and hosted on github. To get the data you can use the git clone command:

git clone https://github.com/gammapy/gamma-cat.git
git clone git@github.com:gammapy/gamma-cat.git

If you don’t have git, you can also fetch the latest version as a zip file as well:

wget https://github.com/gammapy/gamma-cat/archive/master.zip unzip
master.zip # will result in a `gamma-cat-master` folder

Gamma-cat is also shipped in the dataset collection provided by `gammapy download datasets

Getting Started¶

Example how to load a dataset that is distributed with the code in the gammapy repo (i.e. will be available even if you’re offline)

>>> from gammapy.datasets import load_crab_flux_points
>>> flux_points = load_crab_flux_points()

Example how to fetch a dataset from the web (i.e. will download to the Astropy cache and need internet access on first call):

>>> from gammapy.datasets import fetch_fermi_diffuse_background_model
>>> catalog = fetch_fermi_diffuse_background_model()

TODO: explain how the Astropy cache works and make it configurable for Gammapy.

Example how to make a dataset (from scratch, no file is loaded):

>>> from gammapy.datasets import make_test_psf
>>> psf = make_test_psf(energy_bins=20)

Using `gammapy.datasets`¶

tbd

Reference/API¶

gammapy.datasets Package¶

Access datasets.

Functions¶

`load_crab_flux_points`([component])	Load published Crab pulsar and nebula flux points.
`load_diffuse_gamma_spectrum`(reference)	Load published diffuse gamma-ray spectrum.
`load_electron_spectrum`(reference)	Load published electron spectrum.
`load_poisson_stats_image`([extra_info, …])	Load Poisson statistics counts image of a Gaussian source on flat background.
`load_tev_spectrum`(source_name)	Load published TeV flux point measurements.

Classes¶

Datasets([config]) Download and access for all built-in datasets.

Variables¶

gammapy_data Access files from gammapy-data.