taskGNU Astronomy Utilities - Tasks: task #15468, Manage vector values inside tables


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task #15468: Manage vector values inside tables

Submitted by:  Raul Infante-Sainz <infantesainz>
Submitted on:  Mon 18 Nov 2019 10:25:47 AM UTC
Should Start On:  Mon 18 Nov 2019 12:00:00 AM UTC Should be Finished on:  Mon 18 Nov 2019 12:00:00 AM UTC
Category:  Table Priority:  * 5 - Normal
Item Group:  Output not reasonable Status:  None
Privacy:  Public Percent Complete:  0%
Assigned to:  None Open/Closed:  Open
Effort:  0.00
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Mon 18 Nov 2019 01:59:13 PM UTC, comment #1: 

Thanks a lot for bringing this up. This is an interesting format to keep columns with similar values in a FITS table without having to increase the official column number.

Following your task report, it just occurred to me that we can specify sub-columns with a `.N' added to the column name for example in the example you sent, if you wanted the third sub-column of the `apflux_g' column, you can run a command like this:

asttable tractor-0397m080.fits -capflux_g.3

We can similarly extend the concept to Gnuastro's plain-text table format (to easily print on the command-line or create FITS tables with this feature), so the sub-column metadata would be printed like this (the `.M' part is new):


For example, following the example in that section of the book, such, the meta-data for sub-column 3 of column 5 in a table would look like this:

# Column 5.3: column name [km/s,f32,-99] Redshift as speed

Unfortunately I am too busy to implement this now, but it is a very good suggestion to add this feature, I can see many scenarios where such array-column can be very useful. So I just tried to build upon the initial suggestion with some possibly useful implementation details.

Until I get the chance to implement this, if anyone is interested to try implementing it, any help would be very welcome.

Mohammad Akhlaghi <makhlaghi>
Project Administrator
Mon 18 Nov 2019 10:25:47 AM UTC, original submission:  

I found some catalogues (fits tables) that instead one value per each column and row, they are arrays. As a particular example it can be checked the catalogue of DECaLS around NGC1035 (link: https://portal.nersc.gov/project/cosmo/data/legacysurvey/dr8/south/tractor/039/tractor-0397m080.fits).
In this catalogue there are multiple columns, but just focusing on the one with name `apflux_g' it can be seen that there are multiple values for a single object (row). They correspond to photometry measurements on different apertures. When considering this table with the program `Table', it gives as an output a no-sense result.

Consider the column `apflux_g' and the last row, with `asttable':

asttable tractor-0397m080.fits -capflux_g

the result is:


It is a single value. However, the real value is an array (read with `topcat'):

(0.15832691, 0.33208665, 0.523447, 0.87126434, 1.099582, 1.4097637, 1.3801724, 1.514054)

Raul Infante-Sainz <infantesainz>
Project Member


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