Packaging data as a dataset

The dataset framework can represent data from any observatory that has an observatory interface (obs) package in the LSST software stack. This page describes how to create and maintain a dataset.

Creating a dataset repository

Datasets are Git LFS repositories with a particular directory and file structure. The easiest way to create a new dataset is to create an LFS repository, and add a copy of the dataset template repository as the initial commit. This will create empty directories for all data and will add placeholder files for dataset metadata.

Organizing the data

  • The raw directory contains uningested science data. The directory may have any internal structure.
  • The preloaded directory contains a Gen 3 LSST Butler repository with calibration data, coadded difference imaging templates, refcats, and any other files needed for processing science data. The repository must have an <instrument>/defaults collection containing all of the above. It must not contain science data, which belongs only in raw.
  • The config/export.yaml file is a relative-path export of the repository at preloaded, used to set up a separate repository for running ap_verify.
  • The config and pipelines directories contain configuration overrides needed to run the AP pipeline on the data.

The templates and reference catalogs need not be all-sky, but should cover the combined footprint of all the raw images.

Datasets should contain a scripts directory with scripts for (re)generatating and maintaining the contents of the dataset. This allows the dataset, particularly calibs and templates, to be updated with pipeline improvements. The scripts directory is not formally part of the dataset framework, and its exact contents are up to the maintainer.

Documenting datasets

Datasets provide package-level documentation in their doc directory. An example is provided in the dataset template repository.

The dataset’s package-level documentation should include:

  • the source of the data (e.g., a particular survey with specific cuts applied)
  • whether or not optional files such as image differencing templates are provided
  • the expected use of the data

Configuring dataset use

The files in config or pipelines should override any config fields that are constrained by the input data, such as template type (deep, goodSeeing, etc.) or refcat filters, even if the current defaults match. This policy makes the datasets more self-contained and prevents them from breaking when the pipeline defaults change but only one value is valid (e.g., coaddName must be "deep" for a dataset with deep coadds).

Each pipelines directory should contain pipeline files corresponding to the pipelines in the ap_verify/pipelines directory (at the time of writing, ApPipe.yaml, ApVerify.yaml, and ApVerifyWithFakes.yaml). The default execution of ap_verify assumes these files exist for each dataset, though --pipeline can override it.

Configuration settings specific to an instrument rather than a dataset should be handled with ordinary configuration override files.

Registering an observatory package

To ensure dataset processing does not crash, ups/<package>.table must contain a line reading setupRequired(<obs-package>). For example, for DECam data this would read setupRequired(obs_decam). If any other unusual packages are required to process the data, they should have their own setupRequired lines.