2.1. Introduction

This is the AstroData User’s Manual. AstroData is a DRAGONS package. The current chapter covers basic concepts like what is the astrodata package and how to install it (together with the other DRAGONS’ packages). Chapter 2 explains with more details what is AstroData and how the data is represented using it. Chapter 3 describes input and output operations and how multi-extension (MEF) FITS files are represented. Chapter 4 provides information regarding the TagSet class, its usage and a few advanced topics. In Chapter 5 you will find information about the FITS headers and how to access/modify the metadata. The last two chapters, Chapter 6 and Chapter 7 cover more details about how to read, manipulate and write pixel data and tables, respectively.

If you are looking for a quick reference, please, have a look on the Cheat Sheet.

2.1.1. Reference Documents

2.1.2. What is astrodata?

astrodata is a package that wraps together tools to represent internally astronomical datasets stored on disks and to properly parse their metadata using the AstroData and the TagSet classes. astrodata provides uniform interfaces for working on datasets from different instruments. Once a dataset has been opened with astrodata, the object “knows about itself”. Information like instrument, observation mode, and how to access headers, is readily available through the uniform interface. All the details are coded inside the class associated with the instrument, that class then provides the interface. The appropriate class is selected automatically when the file is opened and inspected by astrodata.

Currently astrodata implements a representation for Multi-Extension FITS (MEF) files. (Other representations can be implemented.)

2.1.3. Installing Astrodata

The astrodata package has a few dependencies, Astropy, Numpy and others. The best way to get everything you need is to install Miniconda, and the DRAGONS stack from conda-forge and Gemini’s public conda channel.

astrodata itself is part of DRAGONS. It is available from the repository, as a tar file, or as a conda package. The bare astrodata package does not do much by itself, it needs a companion instrument definitions package. For Gemini, this is gemini_instruments, also included in DRAGONS.

Note

We are in the process of making astrodata an Astropy affiliated package. For now, DRAGONS uses the astrodata integrated with DRAGONS not the affiliated package.

2.1.3.1. Installing Miniforge and the DRAGONS stack

This is required whether you are installing DRAGONS from the repository, the tar file or the conda package.

To avoid duplication, please follow the installation guide provided in the Recipe System User Manual:

2.1.3.2. Smoke test the Astrodata installation

From the configured bash shell:

$ type python
python is hashed (<home_path>/anaconda3/envs/dragons/python)

Make sure that python is indeed pointing to the Anaconda environment you
have just set up.

$ python
>>> import astrodata
>>> import gemini_instruments

Expected result: Just a python prompt and no error messages.

2.1.3.3. Source code availability

The source code is available on Github:

2.1.4. Try it yourself

Try it yourself

Download the data package if you wish to follow along and run the examples presented in this manual. It is available at:

Unpack it:

$ cd <somewhere_convenient>
$ tar xvf ad_usermanual_datapkg-v1.tar
$ bunzip2 ad_usermanual/playdata/*.bz2

Then

$ cd ad_usermanual/playground
$ python

2.1.5. Astrodata Support

Astrodata is developed and supported by staff at the Gemini Observatory. Questions about the reduction of Gemini data should be directed to the Gemini Helpdesk system at https://noirlab.atlassian.net/servicedesk/customer/portal/12 The github issue tracker can be used to report software bugs in DRAGONS (https://github.com/GeminiDRSoftware/DRAGONS).