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.