Cartes du Ciel is free software released under the terms of the
GNU General Public License
Making a map of any part of the sky with all the stars to magnitude 20 was only a dream for many years. Then a few solutions have emerged like USNO-A and USNO-B catalog. The old version of CdC can even get this data online for a limited area but the full USNO-B download was not available.
Now with the release of the much improved PPMXL catalog not only are the files available to everyone but the format allow you can process them immediately for use with CdC!
Its advantage for mapping:
On the inconvenient side:
The PPMXL files available for download at the CDS can be used without transformation by Catgen.
So the following sequence give you the catalog:
This is the only way you can get it, please don't ask me to put the files online for download! But it is easy to share with your friends on an external disk.