NAME

       mOverlaps - Re-project and mosaic your images, with background rectification

SYNOPSIS

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

DESCRIPTION

       Analyze  an image metadata table to determine a list of overlapping images.  Each image is
       compared with every other image to determine all  overlapping  image  pairs.   A  pair  of
       images  are  deemed to overlap if any pixel around the perimeter of one image falls within
       the boundary of the other image.

OPTIONS

       -e     Enables 'exact' overlaps mode, as opposed to the default approximate algorithm. The
              default  mode uses great-circle connecting lines between image corners to determine
              which images overlap. Exact mode will instead check the edge pixels of every  image
              to determine which pixels are inside the others.

              Although the default mode will occasionally report some incorrect overlaps, this is
              not a concern since mDiff will detect and ignore these false positive results  when
              processing the table.

       -d level
              Turns on debugging to the specified level (1 or 2)

       -s statusfile
              Output and errors are sent to statusfile instead of to stdout

ARGUMENTS

       images.tbl
              Table of image metadata generated by mImgtbl.

       diffs.tbl
              Path of output table to be generated containing overlap information.

RESULT

       Output  table contains overlap information for each pair of overlapping images.  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.

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

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.

BUGS

       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"]

       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.

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.