Legacy Survey - Data Access

The Legacy Survey data and database are accessible from the NOAO Data Lab, and from the Legacy Survey team website. Explore the dataset interactively using the Sky Viewer.

Data Lab Table Access Protocol (TAP) service

TAP provides a convenient access layer to the Legacy Survey catalog database. TAP-aware clients (such as TOPCAT) can point to http://datalab.noao.edu/tap. DR3 and DR4 databases are respectively named ls_dr3, and ls_dr4. Select a database in order to see the tables it contains as well as their descriptions. Please note that the data model has changed slightly between DR3 and DR4 so the tables and columns are not identical.

Another way to view the tables is through the Data Lab Query Interface (http://datalab.noao.edu/query.php). From the Column Information tab, select ld_dr3 or ld_dr4 from the left-hand menu to see the list of tables for DR3 or DR4, respectively. Clicking on a table (e.g., ls_dr3.tractor) will show the column names and description.

Data Lab Query Manager

The Query Manager is available as part of the Data Lab software distribution. The Query Manager client provides a Python API to Data Lab database services. For the Legacy Survey DR3 & DR4 releases, these services include anonymous, and authenticated access through synchronous or asynchronous queries of the catalog made directly to the database. Additional Data Lab services for registered users include personal database storage, and storage through the Data Lab VOSpace.

The Query Manager can be called from a Jupyter Notebook on the Data Lab Notebook server. Example notebooks are provided to users upon creation of their user account (http://datalab.noao.edu/register.php)

Image cutouts

The Data Lab Simple Image Access (SIA) service will provide users with a fast way to retrieve cutouts from Legacy Survey images starting with DR5.

Sections of the Legacy Survey can be obtained as JPEGs or FITS files using the Legacy Survey team cutout service, as follows:

DR4:
JPEG:   http://legacysurvey.org/viewer/jpeg-cutout/?ra=190.1086&dec=51.2005&layer=mzls+bass-dr4&pixscale=0.27&bands=grz

FITS:   http://legacysurvey.org/viewer/fits-cutout/?ra=190.1086&dec=51.2005&layer=mzls+bass-dr4&pixscale=0.27&bands=grz

where "bands" is a string like "grz",”gz","g", etc. As of the writing of this documentation the maximum size for cutouts (in number of pixels) is 512. Pixscale=0.262 will return (approximately) the native pixels used by the Tractor.

DR3:
JPEG:   http://legacysurvey.org/viewer/jpeg-cutout/?ra=190.1086&dec=1.2005&layer=decals-dr3&pixscale=0.27&bands=grz

FITS:   http://legacysurvey.org/viewer/fits-cutout/?ra=190.1086&dec=1.2005&layer=decals-dr3&pixscale=0.27&bands=grz

FTP access

The Legacy Survey catalog files, images, and products of the photometric pipeline are available by FTP at the NOAO High Level Data Products site for DR3 and DR4 (guest connection).

NOAO Science Archive access

The NOAO Science Archive portal can be used to retrieve raw, and calibrated Legacy Survey images, as well as the Tractor catalogs.

  • Query the NOAO Science Archive.
  • From the menu of "Available Collections" on the left, select the desired data release (e.g. Legacy Survey-DR3, or Legacy Survey -DR4).
  • Under "Data products - Raw data" check "Object".
  • Optionally, you may select data from specific filters, or restrict the search by other parameters such as sky coordinates, observing date, or exposure time.
  • Click "Search".
  • In the DR3 collection, refine the search by Proposal ID (2014B-0404) in the "Refine" tab in order to obtain DECaLS only images.
The Results page offers several different ways to download the data. See the Tutorials page for details.