Differences

This shows you the differences between two versions of the page.

--- en:news:nomad [2011/11/15 21:26] – effacée pch
+++ en:news:nomad [2018/06/09 15:34] (current) – [Build a catalog for Skychart] pch
@@ Line 1: / Line 1: @@
+~~NOTOC~~
+====== The NOMAD catalog ======
+The  [[http://www.nofs.navy.mil/nomad/|Naval Observatory Merged  Astrometric  Dataset  (NOMAD)]]  contains
+astrometric and photometric data for over 1 billion stars derived from
+the Hipparcos , Tycho-2 ,  UCAC2 ,  and USNO-B1.0
+catalogs for astrometry and optical photometry,  supplemented
+by 2MASS   near-infrared photometry.
+{{ en:news:nomad.png?400|}}
+Thank to the effort of Oleg Maliy we can now use this catalog with Cartes du Ciel!
+The catalog is available to download by Bittorrent. It is presented in the form of text file for each zone area (South Polar Distance).\\
+You need to run Catgen to use this data with Skychart but this as the advantage to let you select the data you need for the catalog size you want.\\
+This also make it easy to use this data outside of Skychart.
+For each star the files contain:
+  * NOMAD identifiers.
+  * A flag for each source catalog.
+  * Coordinates ICRS, with mean error and source flag.
+  * Mean epoch of the position.
+  * Proper motion, with mean error.
+  * Magnitude B, V, R with indication of origin.
+  * Magnitude J, H, K from 2MASS
+  * A flag if the star is a recommended astrometric standard.
+\\
+===== Build a catalog for Skychart =====
+**Update June 9 2018:** A new torrent with working tracker is now available. This version is also fixed for the two data files that where previously in error.
+  - Get the [[http://www.ap-i.net/pub/skychart/nomad/nomad_torrent.zip|zip file]] containing the torrent and a sample Catgen project.
+  - [[wp>BitTorrent_(protocol)|Download all the torrent]], or just the declination zone you need. In this last case beware the zone number are South Polar distance.
+  - Extract every .rar file. (Use [[http://7-zip.org/|7zip]] or on Linux: ls -1 *.rar | xargs -n1 unrar e )
+  - Copy every .txt file to a single directory.
+  - This result in a directory with 1800 .txt files for a total size of 152G.
+  - On Linux/Mac set "ulimit -S -n 20000" see [[en:documentation:catgen#notes_for_linux_and_mac_users|Catgen documentation]]
+  - Launch Skychart
+  - Setup / Catalog / Catgen
+  - Load the sample project: Load Project -> nomad2.prj
+  - Update the input files with your location folder: Input catalog files, click the folder button -> select the 1800 .txt files (be patient until it update the list)
+  - Click the Next button.
+  - On General option page click the Next button.
+  - Review the field list. You can add or remove information here. Click the Next button.
+  - Output directory -> select where to put the catalog.
+  - Click the "Build catalog" button.
+  - Wait a few hours ... (three hours for me). Using the default options the result is 48GB in size.
+  - You can now [[en:documentation:catalog#catalog1|add the catalog]] to Skychart.
+\\
+----
+And a final note: **Please let the torrents active after you finish to download!** We need your upload capacity to make the files available to all on the best condition.