General Instructions

Instructions and Notebooks Specific to Data Set

Need Help?

DC2 Simulated Sky Survey

The DC2 Simulated Sky Survey is a 300-sq-deq simulated survey in six optical bands with observations following a reference LSST observing cadence.

To learn more about the DC2 Simulated Sky Survey, you can read:

Two kinds of datasets are provided: catalogs and images. Follow the instructions below for the type you wish to download. If you use the DC2 Simulated Sky Survey in your work, we ask that you cite both publications above.


NOTE: The catalog collections DC2 Object DPDD dr6 v1 and DC2 Truth Match dr6 v1 are deprecated. Choose the corresponding v2 dataset instead.

Step 1: Download the catalog files

Follow these instructions to download “Object DPDD” or “Truth Match” data files from the DC2 Simulated Sky Survey. You can download the full data set or, if space is at a premium, a recommended subset of files.

The data files you downloaded are in Parquet format, partitioned into sky regions (see Sec. 4.1 of the Release Note for details). You can access these files by standard tools that read Parquet format. We additionally provide a high-level Python package GCRCatalogs to facilitate easy access.

Note that on some very old (e.g., older than 10 years) machines, reading Parquet files may be difficult. If that is a problem for you, please let us know.

Step 2: Prepare GCRCatalogs

See these instructions to install and configure GCRCatalogs.

If you use GCRCatalogs to access the data, please also cite Mao et al. (LSST DESC), ApJS, 234, 36 (2018).

Step 3: Verify access to the data

For the DC2 Object and Truth tables specifically, you can use the following code to print out the tracts that you have downloaded.

import GCRCatalogs

Step 4: Follow the notebooks to access data

You can find examples of using GCRCatalogs in our tutorial notebooks.

If you’re planning to run the example notebooks and don’t already have JupyterLab on your laptop, see these instructions.


Unlike the catalog datasets, it is not possible to choose a subset of the image collection datasets. For a detailed description of the coadded images and associated files included, please see Appendix C of the DESC DC2 Data Release Note.

Two image collections (of different sky coverages) are provided. DC2 coadd dr6 v2 includes all coadded images belonging to tracts 3828 and 3829. DC2 coadd dr6 v2 small includes coadded images for a single patch for each of these tracts.