MOVERLAPS(1)

💖 MOVERLAPS — like, the mOverlaps page, bestie 💖

okay so you opened MOVERLAPS(1) from the Montage manual and honestly? you're in the right place. pull up a chair. 🫶

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✨ NAME ✨

mOverlaps — re-project and mosaic your images, with background rectification 🌈

not me describing a whole pipeline in one line. iconic behaviour, honestly.

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🌸 SYNOPSIS 🌸

mOverlaps [-e] [-d level] [-s statusfile] images.tbl diffs.tbl

that's it. that's the whole vibe check. 💅

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🦋 DESCRIPTION 🦋

so basically mOverlaps takes an image metadata table and figures out which images overlap each other. it goes full main-character and compares every image against every other image, so you get a complete list of overlapping pairs. no cap.

and when do two images count as overlapping? a pair is deemed to overlap if any pixel around the perimeter of one image falls within the boundary of the other image. that's the rule. that's the whole test. ✨

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🎀 OPTIONS 🎀

• -e — turns on 'exact' overlaps mode, as opposed to the default approximate algorithm. the default mode uses great-circle connecting lines between image corners to work out which images overlap. exact mode is the overachiever: it actually checks the edge pixels of every image to figure out which pixels are inside the others. 💅

lowkey important: although the default mode will occasionally report some incorrect overlaps, this is not a concern, because mDiff will detect and ignore these false positive results when it's processing the table. so like. breathe. 😌

• -d level — turns on debugging to the specified level (1 or 2)
• -s statusfile — output and errors get sent to statusfile instead of to stdout

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🍓 ARGUMENTS 🍓

• images.tbl — table of image metadata generated by mImgtbl.
• diffs.tbl — the path of the output table to be generated, containing overlap information.

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⭐ RESULT ⭐

the output table contains overlap information for each pair of overlapping images. here's the tea on its columns: the first two columns are integer identifiers for the images from images.tbl; the second two give their filenames; and the final column shows the filename of the FITS file that will be generated using mDiffExec. 🫶

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💜 MESSAGES 💜

OK     [struct stat="OK", countnum-overlaps]

ERROR  Cannot open status file: statusfile

ERROR  Failed to open output filename

ERROR  Invalid image metadata file: filename

ERROR  Not enough information to determine coverages (CDELTs or CD matrix)

ERROR  Need columns: cntr ctype1 ctype2 nl ns crval1 crval2 crpix1 crpix2 cdelt1 cdelt2 crota2 fname (equinox optional)

ERROR  Bad WCS for image n

yeah she will absolutely tell you what's wrong. read the messages, bestie, they're not decorative. 😭

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🌈 EXAMPLES 🌈

the following example looks at a list of 16 images, described in images.tbl, and calculates which images overlap:

$ mOverlaps images.tbl diffs.tbl
       [struct stat="OK", count=42]

Output file: diffs.tbl.

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💀 BUGS 💀

okay so this is the part where we hold hands. 🫶

• the drizzle algorithm has been implemented but has not been tested in this release.
• if a header template contains carriage returns (i.e., created/modified on a Windows machine), the cfitsio library will be unable to read it properly, resulting in the error:

[struct stat="ERROR", status=207, msg="illegal character in keyword"]

🙈 windows line endings really said "let me ruin your whole afternoon".

• it is best for the background correction algorithms if the area described in the header template completely encloses all of the input images in their entirety. if parts of input images are "chopped off" by the header template, the background correction will be affected. we recommend you use an expanded header for the reprojection and background modeling steps, returning to the originally desired header size for the final coaddition. the default background matching assumes that there are no non-linear background variations in the individual images (and therefore in the overlap differences). if there is any uncertainty in this regard, it is safer to turn on the "level only" background matching (the -l flag in mBgModel).
• mOverlaps generates a list of images whose outer boundaries overlap. this does not guarantee that any image pixels within those images actually overlap; the overlap regions may only contain blank pixels, especially in images that have been rotated a significant amount. 💀
• this eventually will result in a number of images showing up as "failed" when running subsequent programs like mDiffExec, but this will not have any effect on the final mosaic. so like. don't panic. ✨

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👑 COPYRIGHT 👑

2001-2015 California Institute of Technology, Pasadena, California

if your research uses Montage, please include the following acknowledgement: "This research made use of Montage. It is funded by the National Science Foundation under Grant Number ACI-1440620, and was previously funded by the National Aeronautics and Space Administration's Earth Science Technology Office, Computation Technologies Project, under Cooperative Agreement Number NCC5-626 between NASA and the California Institute of Technology."

the Montage distribution includes an adaptation of the MOPEX algorithm developed at the Spitzer Science Center. 🧚

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okay and that's the page!! this is Montage 5, from Dec 2016, and yeah she's still serving MOVERLAPS(1) energy. go overlap some images, bestie, you're gonna slay 💅💖🌸