Tycho-2 display

Roger Pickard May 17, 2001

Hi folks,
Some time ago Bill wrote as follows:-

<<TYCHO-2 DISPLAY:
Mark Elowitz asked about Tycho-2 display in Guide 7, using the
Tycho-2 disk. Yes, you could do that using a .TDF file. One slight
difficulty is that the file is sorted by GSC identifier, and not RA.
This means that Guide would have to read through the entire file for
each redraw, and it's a 500 MByte monster. Non-programmers may wish
to skip the following:
The "fix" to this would probably be to have a utility to extract a
desired RA/dec rectangle of data from the file, and have Guide show
that instead. This utility would take the RA/dec rectangle data,
figure out which GSC tiles are involved in that area, and extract
them from the catalog. If you want to do this, the Charon C/C++
source code, described and available here:
http://www.projectpluto.com/source.htm#charon
has certain components you may find useful (actually, they'll
do 90% of the job for you). In particular, take a look in the
grab_tycho2_data( ) function in 'grab_gsc.cpp'; it was added specifically
to let Charon do Tycho-2 based astrometry.
You'll also need the code to figure out which GSC tiles cover a given
area; that's in 'regions3.cpp'. It should be a straightforward job...
and the resulting utility would be useful to a lot of people, I think.>>

As I now have the Tycho-2 CD I was wondering if anybody has indeed
written this exceedingly useful utility?
Regards,
Roger
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Roger Pickard