Using your own local catalogues

If you have a simple text file containing columns of positions then the most straight-forward way to plot them in GAIA is by using the `Select Positions...' toolbox. This accepts (as do the various astrometry toolboxes) a file containing the following values:

ID  RA  DEC  X  Y

in that order, e.g.

1   00:19:49.47   00:07:25.9   854    50
2   00:20:06.71   00:06:05.3   240   244
3   00:19:47.54   00:04:23.2   925   484
4   00:19:58.07   00:04:49.1   549   424
5   00:19:48.69   00:06:59.0   882   114

The columns should be space separated and the celestial coordinates should be in decimal degrees, or sexagesimal format as shown above. More complex files can be imported into this toolbox using its `Import text file...' option (this allows fixed column widths or other separators). If you need to import such a file into a catalogue window, (this is the sort of window that queries to on-line catalogues are shown in, and provide extra facilities like applying intensity cuts etc.) then use the Import plain text file... toolbox from the Positions... menu.

You can also create your own local catalogues in TST format. This allows you to describe how to plot the catalogue. For instance if you wanted to plot position vectors as correctly orientated lines over an image you would need a tab table that contained the following sort of information (again note that the <TAB> string should be replace by a single tab character):

# File created by: pwd on June 15, 1999 at 10:24:04
id_col: 0
x_col: 1
y_col: 2
symbol: {ID LENGTH ANGLE} {line {} {} {$ANGLE+27.0} {} {}} {{$LENGTH*0.1} {}}
#
ID <TAB>    XPOS    <TAB> YPOS    <TAB> LENGTH   <TAB>  ANGLE
--          ----          ---           ------          -----
ID#1 <TAB>  206.000 <TAB> 189.000 <TAB> 6.32528  <TAB>  104.816
ID#2 <TAB>  209.000 <TAB> 189.000 <TAB> 5.86891  <TAB>  109.238

The x_col and y_col parameters indicate the columns of the data that correspond to the X and Y positions and the symbol parameter how to plot a line centered on that position. In this case the statements says extract values for the ID, LENGTH and ANGLE columns, then draw lines with position angle ANGLE+27 and length LENGTH$*$0.1 pixels. Note that a dollar sign is used to prefix column names in these expressions (in fact these expressions will be parsed by the Tcl ``expr'' command, with the column values set to a variable with the same name as the column for each line in the table).

Creating such a symbol parameter is best done by using the special Set Plot Symbols... window, available under the local catalogue menu Options. Using this window you can plot multiple symbols per object, specify which column to use as labels, change the graphic colour etc.. Now if you look in the file ~/.skycat/skycat.cfg after setting up your options a suitable symbol parameter is recorded together which the description for your local catalogue (which you can then edit into your tab files).

To find out more about the TST format and how to configure plot symbols you should consult the ESO document `Astronomical Catalog Library' and `Writing Catalogue and Image Servers for GAIA and CURSA ' (SSN/75).