[gnuastro-devel] [task #13557] WCS meta-data of many images in a table

[Mohammad Akhlaghi]

Update of task #13557 (project gnuastro):

                Category:                    Crop => All Gnuastro           
                Priority:               1 - Later => 7 - High               
                 Summary: Read image meta-data from file => WCS meta-data of
many images in a table

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Follow-up Comment #1:

Updated statement: In some contexts it is necessary for Gnuastro's programs to
load the WCS meta-data of many files. One example can be using Crop's WCS-mode
cropping which can stitch many images if the object lies on the border of
multiple images. Another can be MakeCatalog when it wants to map the
segmentation map on a region in the border of another image (not yet fully
implemented). 

In surveys (where the reduced image is broken into tiles), the WCS structure
is already matched between all the images. With only certain elements
differing. Having to parse/convert the FITS keywords of all the files in every
run of every program can be very inefficient or even impractical (especially
on large surveys like LSST). To solve this problem, we can parse all the
images once and make a FITS table. In its header, we can write a reference WCS
structure and in each row, we can have the values that need to be changed for
each input along with the file/extension of each. Afterwards, any program can
only to translate one set of FITS keywords into an internal WCS structure, and
parse the table to find which image it needs (has an overlap with the region
it wants) for its higher-level processing.

Before writing, the table can also be sorted in a specific way to help user
programs find the images they want more efficiently (without having to check
all the table).

This can be implemented as a library feature to be used in all programs and
also by users in their own programs.

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