UCAC4 permanently in Guide

Bill J Gray Oct 9 8:46 AM

Hi Denis,

> Are you planning to take the UCAC4 permanently into Guide 9? With all
> the improvements, it would be worth to create the a new Guide 9 set of
> files as you did for UCAC3. The best way would be to create codes to
> convert UCAC4 to Guide 9 format and use the resulting files to replace
> the UCAC3 360 files.

I expect to do that at some point. First step has been to get Guide
to show UCAC4 from the original disks. This serves several purposes,
one of which is that anybody (including Guide 8 users) can get UCAC4
displaying as soon as they have the UCAC4 disks.

Another advantage: in order to get UCAC3 to fit on the Guide 9 DVD,
I had to compress it, and the compression was not lossless. I reduced
the precision (usually to a point well within the error levels of the data)
and threw out some internal flags and similar "less important" data.
I'll have to do the same sort of things with UCAC4. If you run from the
raw data, you get absolutely everything. (If you look at "more info"
for UCAC4, you'll see that there is quite a lot of data: three infrared
magnitudes from 2MASS, two magnitudes from UCAC4 itself, and -- for a
lot of brighter stars -- five APASS magnitudes. Be warned that these last
are not to be trusted to the degree their errors indicate, though.)

> If I had the codes I would give it a try. Are the codes to access the
> reformatted ucac3 in guide 9 available?

I haven't gotten those posted yet (I have a _lot_ of code that needs
to be posted... it also needs to be commented and cleaned up to the point
where it won't drive anyone too crazy). I _do_ have C code posted for
accessing the raw UCAC4, 3, and 2 data, at


This code should be quite readable and, I hope, useful to any C or
C++ programmers out there.

-- Bill