Help for DEMFIX

PURPOSE

     demfix fills in holes in a DEM (Digital Elevation Model)
     using another digital elevation model.  Both must have 
     Geotiff labels.  An example would be to fix holes in a 
     SAR image (due to layover or water) using DTED level I.
     
     The images must be in the same map projection but can
     have different scales and offsets.  It is desirable but
     not necessary for the secondary image to cover the area
     of the image being fixed, or at least the part of the 
     image containing holes.
     
     A connected component detects connected holes and their
     boundary pixels.  The corresponding patch from the other
     image is generated.  It is compared at the edge pixels 
     and a "boost" value is calculated to align the patches.
     The patch from the other image might have non-aligned
     pixels so bilinear interpolation is used to find the 
     best value for the pixel centers in the primary image.
     
     If the second image does not cover a patch, the pixel 
     value is calculated by 1/n interpolation on all of the
     edge pixels of the primary image.  You could think of
     of this as a "soap bubble film" covering the patch.
     
     An ocean threshold is provided that will use the second-
     ary input to mask out the ocean areas.  For SAR data
     a value of 20 is recommended.  All SAR values less than
     20 and the secondary input is zero (nearest neighbor)
     will convert to zero.  Do not use this parameter if
     ocean is not present.  IF YOU DO NOT USE THIS PARAMETER
     IN AN OCEAN AREA, THE PROGRAM WILL RUN FOR A LONG TIME OR
     POSSIBLY FAIL.
     
     Note on images with gores (such as aster).  Make the gore
     value greather than the threshold (using photoshop if
     necessary).  Then the gores will be left alone.  If a hole
     is on the edge of the data, then the hole and the gore will
     interact, the hole interpolating in some of the gore value.
  
TAE COMMAND LINE FORMAT

     demfix INP=(A,B) OUT=C THRESH=N 

     where

     A                   is a digital elevation model with 
                         "holes".
     B                   is a digital elevation model with 
                         values to fill the holes.
     C                   is a copy of A with the holes filled
     N                   is the integer value that defines 
                         holes in the image A.  Values less
                         than or equal N is part of a hole.
OPERATION
     demfix fills in holes in a DEM (Digital Elevation Model)
     using another digital elevation model.  Both must have 
     Geotiff labels.  An example would be to fix holes in a 
     SAR image (due to layover) using DTED level I.
     
     The images must be in the same map projection but can
     have different scales and offsets.  It is desirable but
     not necessary for the secondary image to cover the area
     of the image being fixed, or at least the part of the 
     image containing holes.
     
     A connected component detects connected holes and their
     boundary pixels.  The corresponding patch from the other
     image is generated.  It is compared at the edge pixels 
     and a "boost" value is calculated to align the patches.
     The patch from the other image might have non-aligned
     pixels so bilinear interpolation is used to find the 
     best value for the pixel centers in the primary image.
     The boosted patch is adjusted by the residual differences
     of edge pixels around the hole.  All the residuals are
     weighted by 1.0/distance-squared from each pixel in the hole
     so the patch will smoothly meet the primary DEM at all of
     the edges.
     
     If there is no second image, the pixel value is calculated
     by 1/n**2 interpolation on all of the edge pixels of the primary
     image.  You could think of this as a "soap bubble film"
     covering the patch (though not exactly).
     

WRITTEN BY:                   Al Zobrist         28 JUL 02
COGNIZANT PROGRAMMER:         Al Zobrist
Revisions:
  2008-01-10 WLB Switched to USES_ANSI_C AND LIB_CARTO; misc cleanup
  2015-11-19 WLB Migrated to MIPL
  2019-08-22 WLB IDS-7922 - initialized a bunch of variables.
  2022-07-14 B. Crocco afids to opensource