Reconstruct an original UCAC2 catalog from Vizier input files  

(How to download the UCAC2 from internet)

The United States Naval Observatory is currently conducting an ongoing astrometric observation project. The second public release of data from this project is the UCAC2 catalog. The UCAC2 is a high density, highly accurate, astrometric catalog of 48,330,571 stars covering the sky from -90 to +40 degrees in declination and going up to +52 degrees in some areas. Download also the new intermediate UCAC2 supplement to +90 degrees !!

Example data files (z001 to z007), as well as the unformatted index file (u2index.da) and TXT format index file u2index.txt can be downloaded from the USNO anonymous ftp server ftp://pisces.usno.navy.mil/pub/nz

The UCAC2 is by the USNO free distributed by CD ROM. It is possible this service will be discontinued.  For people having a fast internet connection, they can reconstruct the catalog from VIZIER input files.

The following is a guide to reconstruct the original 2 Gbyte large UCAC2 catalog from VIZIER input files:

Step #1 - Obtaining the UCAC2 Catalog Data from internet

The UCAC2 catalog is stored in a compressed binary format at  http://badc.lamost.org/archives/UCAC2/bindat/   or http://vizier.hia.nrc.ca/viz-bin/ftp-index?/ftp/cats/bincats/UCAC2/bindat 1)  You will need to download the 288 binary files (z001.bin - z288.bin) from the UCAC2 folder. (Each file is covering an declination band of 0.5 degrees starting with Z001 for -90 to -89.5 degrees.)

The entire catalog is roughly 1.6 Gbyte large and requires a fast internet connection. Place all the *.bin files in one folder (e.g. C:\UCAC2).

Note 1): Used to be ftp://vizier.cfa.harvard.edu/pub/cats/bincats/UCAC2/bindat/ but no longer available.

Step #2 - Download and run the conversion software (Windows 95...XP)

Download the makeucac.zip file, which contains the software necessary to convert the catalogs from their binary format to a TXT format and then to reconstruct the original UCAC2 files It also contains the orginal binary index file u2index.da. Unpack the files in the same folder (e.g. C:\UCAC2).

- Run the batch file TO_TXT.BAT.   This will use DECODE.EXE to convert all .BIN files to ASCII/ TXT files and requires more then 6 Gbytes free disk space.

- Run the MAKEUCAC2.EXE utility.  This will make from the TXT files the original Z001 to Z288 files. This requires an additional 2 Gbyte of disk space

The catalog is then ready. The .BIN and .TXT files can be deleted. The catalog files are Z001 to Z288 and the provided indexfile U2index.da. If your running low in disk space you should convert the catalog in smaller steps. E.g. file Z001 to Z050 first. To test the first files, zoom in to the celistial south pole and switch on the UCAC2. Delete the files with size zero created during conversion otherwise you will get a stream error message.

Some programs need the TXT version of the index file called u2index.txt  rather then the binary u2index.da index file. Download it from: http://badc.lamost.org/archives/UCAC2/info/

The file sizes in bytes of the first files are as follows:

 31,916 z001.bin,       15,846 z001.txt,             38,544 z001,

 96,540 z002.bin,       352,786 z002.txt,            117,524 z002,

164,972 z003.bin,       603,720 z003.txt,            201,168 z003

Remarks:

1) Since in the "Vizier input files" the original RA proper motion is divided by cos(dec), it has to be transformed back to the original value. There will be small rounding errors compared with the original UCAC2 files. The MAKEUCAC2 program converts the RA proper motion back to the original format but can't recreate exactly the original due these rounding errors.

2) Most likely there will be the possibility to get the UCAC2 CD-roms by postal mail, organized by Bill J Gray of Project Pluto:

,,If USNO _does_ run out, as happened for A1.0 and A2.0, I will almost certainly start distributing UCAC2 at no charge. The method would be the same "copy the disks and pass them along" scheme that I'm already using for A2.0: http://www.projectpluto.com/a2_pass.htm "

Note 2006-3-9:  The program makeucac2.exe is now at version 1.0a.  John Irwin indicated that some fields not used in HNSKY to display stars where converted using byte instead of a shortinteger This is now fixed. The differences occured in the 1-byte fields (items 4,5,7,14-17,22,23) which are meant to contain signed integers with an offset of 127.

Feedback is welcomed.

Success

Some screen shots using the UCAC2 in the HNSKY planetarium program