Question

怎么下载DESI-EDR的光谱，在哪里可以找到相应的catalog

Answer 1

Please see the answer in this thread: https://help.desi.lbl.gov/index.php?qa=52&qa_1=process-to-download-edr-data

Answer 2

and this page contains useful information about desi programs and healpix: https://data.desi.lbl.gov/doc/organization/

Answer 3

i have never downloaded data from the public database, but i think the following link works. For example, from the link below

https://data.desi.lbl.gov/doc/access/

you can find The SPectra Analysis and Retrievable Catalog Lab (SPARCL) service and then go to the ftp page.

https://data.desi.lbl.gov/public/edr/

spectra is stored at paths like: https://data.desi.lbl.gov/public/edr/spectro/redux/fuji/healpix/sv1/bright/49/4957/

Here sv1 bright means the sv1 program observed at bright time. You can also go to other programs. 49 is the healpix number. Under each folder named with different healpix numbers, you can find multiple folders that store the spectra

Note here given a healpix number, it can be converted to the central ra and dec through:

https://healpy.readthedocs.io/en/latest/generated/healpy.pixelfunc.ang2pix.html#healpy.pixelfunc.pix2ang

Answer 4

To download DESI-EDR data, use the desi_get_dr_subset script with these simple steps:

1. Clone the repository if you don't have it:

   git clone https://github.com/desihub/desida.git
   cd desida/bin
   

2. Run the script with EDR flag:

   python desi_get_dr_subset --dr edr
   

This will download EDR data centered on the default coordinates (RA=179.6, Dec=0.0) which corresponds to the Rosette 1 field. It will:

• Download the redshift catalog
• Find the healpix with most targets in that region (typically 26965)
• Download all spectra for that healpix
• Download associated tile data

The data will be saved to a folder called ./tiny_edr in your current directory. If you need data from a different sky region, you can specify coordinates with --ra, --dec, and --radius parameters.