#!/usr/bin/perl
use FileHandle;
use File::Basename;
use List::Util qw(first max maxstr min minstr reduce shuffle sum);
use Getopt::Long;

$npoly = 3;	#offset polynomial order
$rlks = 1;
$azlks = 1;
$rpos = "-";
$azpos = "-";
$rflag = 0;
$sc = 0.8;
$exp = 0.4;
$blksz = "512";
$mflg = 1;	#turn on generation MLI-1 in the geometry of MLI-2 by default

$thres_mli = 7.0;	#SNR threshold for accepting MLI offset measurement
$thres_slc = 7.0;	#SNR threshold for accepting SLC offset measurement
$rpatch = 128;		#SLC range patch size
$azpatch = 256;	        #SLC azimuth patch size
$rwinm = 256;		#MLI range patch size
$azwinm = 256;		#MLI azimuth patch size
$patch = 1024;		#init_offsetm patch size
$snr_min = 7;

GetOptions ('b=i' => \$blksz, 'e=f' => \$exp, 's=f' => \$sc, 'm' => \$mflg,'n=i' => \$npoly,'t=f' => \$thres_slc);

if (($#ARGV + 1) < 9){die <<EOS ;}
*** $0
*** Copyright 2015, Gamma Remote Sensing, v5.9 26-Apr-2015 clw ***
*** Resample a set of SLCs to a common reference SLC using a lookup table and DEM ***

usage: $0 <SLC_tab> <ref_SLC> <ref_SLC_par> <ref_MLI_par> <DEM_rdc> <MLI_dir> <RSLC_dir> <RSLC_tab> <mode> [rflag] [rlks] [azlks] [rpos] [azpos] [patch] [snr_min]

    SLC_tab      (input) two column list of SLC filenames and SLC parameter filenames (including paths) (ascii)
    ref_SLC      (input) reference SLC (including path)
    ref_SLC_par  (input) ISP image parameter file of the reference SLC (including path)
    ref_MLI_par  (input) ISP image parameter file of the reference MLI (including path)
    DEM_rdc      (input) DEM in Range-Doppler Coordinates with width and height as described in the MLI_par
    MLI_dir      (input) directory containing MLI parameter files, same the same width and height as DEM_rdc.
    RSLC_dir     directory to contain the resampled SLCs, lookup tables, ISP image parameter files, and log files   
    RSLC_tab     (output) RSLC_tab file for the resampled SLC files  
    mode         processing modes:
                   0: generate lookup table and resample MLI-1 image into the geometry of MLI-2
                   1: refine lookup table based on measured offsets between MLI-1 resampled to the geometry of MLI-2 (optional)
                   2: resample SLC-2 to the geometry of the reference SLC using lookup table    
                   3: create offset parameter files for SLC resampling refinement, measure offsets, and calculate the SLC offset fit polynomials
	           4: resample SLC images using lookup table offsets determined in mode 3 and generate RSLC_tab
    rflag        flag for interative refinement of the resampled SLC:
                   0: resample and measure residual range and azimuth offsets  (no interation, default)
		   1: interatively improve range and azimuth offset polynomials then measure residual offsets
    rlks         number of range looks for initial MLI offset estimation  (enter - for default: $rlks)
    azlks        number of azimuth looks for initial MLI offset estimation  (enter - for default: $azlks)
    rpos         center of patch for initial MLI offset estimation range (samples) (enter - for default: image center)
    azpos        center of patch for initial MLI offset estimation azimuth (lines) (enter - for default: image center)
    patch        patch size for initial MLI offset estimate (enter - for default: $patch)
    snr_min      SNR threshold to accept the initial MLI offset estimate (enter - for default: $snr_min)
    -m           (option) generate MLI-1 in geometry of MLI-2, required for optional refinement of lookup table using MLI-1 and MLI-2)
    -b blksz     (option) number of lines/block, only required for spotlight-mode SAR where there are along-track changes in the Doppler centroid, minimum value: 64
    -n npoly     (option) number of terms in the range and azimuth offset polynomials (npoly: 1,3,4,6) (default: $npoly)
    -t thres     (option) SNR theshold to accept an SLC offset measurement (default: $thres_slc) 
    -s scale     (option) set image display scale factor (default: $sc)   
    -e exp       (option) set image display exponent (default: $exp)
EOS

open(SLC_TAB, "<$ARGV[0]") or die "\nERROR $0: table of SLC images and parameter files does not exist: $ARGV[0]\n\n";
print "SLC_tab table of SLC images and parameter files: $ARGV[0]\n"; 

$ref_slc1 = $ARGV[1];
$ref_par1 = $ARGV[2];
$ref_MLI_par = $ARGV[3];
$dem_rdc =  $ARGV[4];
$mli_dir =  $ARGV[5];
$rslc_dir = $ARGV[6];
$rslc_tab = $ARGV[7];

$mode = $ARGV[8];
($mode >= 0 && $mode <= 6) or die "\nERROR $0: invalid mode for script: $mode\n\n";
print "$0 mode: $mode\n";

if($#ARGV >= 9){$rflag = $ARGV[9];}
if($#ARGV >= 10){$rlks = $ARGV[10];}
if($#ARGV >= 11){$azlks = $ARGV[11];}
if($#ARGV >= 12){$rpos = $ARGV[12];}
if($#ARGV >= 13){$azpos = $ARGV[13];}
if($#ARGV >= 14){$patch = $ARGV[14];}
if($#ARGV >= 15){$snr_min = $ARGV[15];}

printf "reference SLC: $ref_slc1\n";
printf "reference SLC parameter file: $ref_par1\n";
printf "reference MLI parameter file: $ref_MLI_par\n";
printf "resampled SLC directory: $rslc_dir\n";
printf "DEM in range-Doppler coordinates: $dem_rdc\n";
printf "MLI data directory: $mli_dir\n";
printf "output table for resampled SLCs: $rslc_tab\n\n";

-e $ref_slc1 or die "\nERROR $0: reference SLC does not exist: $ref_slc1\n";
-e $ref_par1 or die "\nERROR $0: ISP image parameter file of the reference SLC does not exist: $ref_par1\n";
-e $ref_MLI_par or die "\nERROR $0: ISP image parameter file of the reference MLI does not exist: $ref_MLI_par\n";
-d $mli_dir or die "\nERROR $0: directory containing MLI images and parameter files does not exist: $mli_dir\n";
-e $dem_rdc or die "\nERROR $0: DEM in range doppler coordinates does not exist: $dem_rdc\n";

unless (-d $rslc_dir){
  print "creating resampled SLC directory: $rslc_dir\n";
  (mkdir $rslc_dir) or die "ERROR $0: non-zero exit status, could not create SLC data directory $rslc_dir\n";
}

$log = "$rslc_dir/SLC_resamp_lt_all"."_$mode".".log"; 
open(LOG,">$log") or die "ERROR $0: cannot open log file: $log\n";
LOG->autoflush;  
print LOG "$0 @ARGV\n\n";	#print command line that was used

if ($mode == 4){
  open(RSLC_TAB, ">$rslc_tab") or die "ERROR $0: cannot open RSLC_tab file: $rslc_tab\n\n";
}

$time = localtime;
print LOG "*** $0 processing start: $time ***\n";
print "*** $0 processing start: $time ***\n";
print "log file: $log\n";

my ($s1, $dir1, $ext1) = fileparse($ref_slc1, qr/\.[^.]*/); #extension is the last bit after the last period 
$ref_id = $s1;
$ref_slc = "$rslc_dir/$s1.rslc";
$ref_par = "$rslc_dir/$s1.rslc.par";
close LOG;

unless (-e $ref_slc) {		#copy reference slc and slc parameter file if they do not yet exist
  execute("cp $ref_slc1 $ref_slc",$log);
}
  
unless (-e $ref_par){
  execute("cp $ref_par1 $ref_par",$log);
}

@width = extract_param($ref_par,"range_samples:");
@lines = extract_param($ref_par,"azimuth_lines:");

#determine the number of range and azimuth patches for measuring offsets, minimum 8x16 grid
$nrp = min(int($width[1]/($rpatch/2) + 0.5), 64);
if ($nrp < 8) {
  $nrp = 8;
}
$nazp = min(int($lines[1]/($azpatch/2) + 0.5), 64);
if ($nazp < 16) {
  $nazp = 16;
}

open(LOG,">>$log") or die "ERROR $0: cannot open log file: $log\n";
LOG->autoflush;

@mli1_width = extract_param($ref_MLI_par,"range_samples:");
@mli1_lines = extract_param($ref_MLI_par,"azimuth_lines:"); 
@mli1_rlks = extract_param($ref_MLI_par,"range_looks:");
@mli1_azlks = extract_param($ref_MLI_par,"azimuth_looks:");

$nrpm = min(int($mli1_width[1]/($rwinm/2) + 0.5), 64);		#number of range and azimuth patches for MLI matching
if ($nrpm < 8) {
  $nrpm = 8;
}
$nazpm = min(int($mli1_lines[1]/($azwinm/2) + 0.5), 128);
if ($nazpm < 8) {
  $nazpm = 8;
}

if ($rpos eq "-") {
  $rpos = int($mli1_width[1]/2);
}
if ($azpos eq "-") {
  $azpos = int($mli1_lines[1]/2);
}

($s1, $dir1, $ext1) = fileparse($ref_MLI_par, qr/\.[^.]*/);	#extension is the last bit after the last period
$ref_MLI = $dir1."/".$s1;
 
$time = localtime;
print LOG "resampled RSLC data directory:$rslc_dir\n";
print LOG "reference SLC: $ref_slc\n";
print LOG "reference SLC parameters: $ref_par\n";
print LOG "reference SLC range samples: $width[1]  azimuth lines: $lines[1]\n";
print LOG "\nreference MLI: $ref_MLI\n";
print LOG "reference MLI parameters: $ref_MLI_par\n";
print LOG "reference MLI range samples: $mli1_width[1]\n";
print LOG "reference MLI range looks: $mli1_rlks[1]  azimuth looks: $mli1_azlks[1]\n";
print LOG "output RSLC_tab file: $rslc_tab\n\n";
print LOG "initial MLI offset patch center range: $rpos   azimuth: $azpos\n";
print LOG "initial MLI offset patch size: $patch\n";
print LOG "SLC range patch size: $rpatch  azimuth patch size: $azpatch\n";
print LOG "number of SLC range patches: $nrp   azimuth patches: $nazp\n";
print LOG "MLI range patch size: $rwinm  azimuth patch size: $azwinm\n\n";
print LOG "number of MLI range patches: $nrpm   azimuth patches: $nazpm\n";
print LOG "SNR threshold to accept MLI offset measurement: $thres_mli\n";
print LOG "SNR threshold to accept SLC offset measurement: $thres_slc\n";
($rflag == 0) or print "measuring offsets with respect to the resampled SLC\n";

print "resampled RSLC data directory: $rslc_dir\n";
print "reference SLC:  $ref_slc\n";
print "reference SLC parameters:    $ref_par\n";
print "reference SLC range samples: $width[1]  azimuth lines: $lines[1]\n";
print "\nreference MLI: $ref_MLI\n";
print "reference MLI parameters: $ref_MLI_par\n";
print "reference MLI range samples: $mli1_width[1]\n";
print "reference MLI range looks: $mli1_rlks[1]  azimuth looks: $mli1_azlks[1]\n";
print "output RSLC_tab file: $rslc_tab\n\n";
print "initial MLI offset patch center coordinates range: $rpos   azimuth: $azpos\n";
print "initial MLI offset patch size: $patch\n";
print "SLC range patch size: $rpatch  azimuth patch size: $azpatch\n";
print "number of SLC range patches: $nrp   azimuth patches: $nazp\n";
print "SNR threshold to accept SLC offset measurement: $thres_slc\n";
print "MLI range patch size: $rwinm  azimuth patch size: $azwinm\n";
print "number of MLI range patches: $nrpm   azimuth patches: $nazpm\n";
print "SNR threshold to accept MLI offset measurement: $thres_mli\n";

($rflag == 0) or print "rflag = 1: measuring offsets relative to the resampled SLC to improve the offset model\n";
close LOG;

open(OFFINP, ">create_offset.in") or die "ERROR $0: cannot create file with inputs to create_offset: create_offset.in\n";
print OFFINP "SLC offset parameters\n0 0\n$nrp $nazp\n$rpatch $azpatch\n$thres_slc\n0\n".$width[1]."\n";
close OFFINP;
$k = 0;

LINE: while (<SLC_TAB>) {     #read lines of processing list file
  $time = localtime;
  chomp $_;		      #remove new line from record
  next LINE if /^$/;	      #skip blank lines in processing list
  next LINE if /^#/;	      #skip comments in processing list
  @fields = split;	      #extract the scene identifier and other parameters on the line if present

  $slc2 = $fields[0];
  $slc2_par = $fields[1];
  -e $slc2_par or die "ERROR $0: ISP image parameter file does not exist for slc2: $slc2_par\n";
  -e $slc2 or die "ERROR $0: slc2 image file does not exist: $slc2\n";     
  @width2 = extract_param($slc2_par,"range_samples:");
  @lines2 = extract_param($slc2_par,"azimuth_lines:"); 

  my ($s2, $dir2, $ext2) = fileparse($slc2, qr/\.[^.]*/); #extension is the last bit after the last period 
  $rslc = "$rslc_dir/$s2.rslc";
  $rslc_par = "$rslc_dir/$s2.rslc.par";
  $slc2_id = $s2;

  $mli1_par = $ref_MLI_par;
  $mli2 = "$mli_dir/$slc2_id.mli";   
  unless (-e $mli2){
    $mli2 =  "$mli_dir/$slc2_id.rmli";
  }
  $mli2_par = "$mli_dir/$slc2_id.mli.par";
  unless (-e $mli2_par){
    $mli2_par = "$mli_dir/$slc2_id.rmli.par";
  }
  @mli2_width = extract_param($mli2_par,"range_samples:");
  @mli2_lines = extract_param($mli2_par,"azimuth_lines:");

  if($ref_id eq $slc2_id){	#in the case of SLC-2 is the reference scene , jump to the next scene
    printf RSLC_TAB "$ref_slc  $ref_par\n";	#output RSLC_tab reference SLC record
    next;
  }
  $k = $k + 1;  
  $id = $ref_id."_".$slc2_id;	
  $off = "$rslc_dir/$id.off";		#offset parameter file for offset parameters between SLC data
  $lt0 = "$rslc_dir/$id.lt0";		#initial lookup table 
  $lt1 = "$rslc_dir/$id.lt1";		#refined lookup table  
  $offs = "$rslc_dir/$id.offs";		#binary offsets
  $coffs = "$rslc_dir/$id.coffs";	#culled offsets
  $offs_lt0 = "$rslc_dir/$id"."_lt0.offs";	#binary offsets for MLI offsets
  $coffs_lt0 = "$rslc_dir/$id"."_lt0.coffs";	#culled offsets for MLI offsets
  $snr_lt0 = "$rslc_dir/$id"."_lt0.snr";	#SNR for MLI offsets
  $snr = "$rslc_dir/$id.snr";
  $mli1_lt0 = $rslc_dir."/".$id."_lt0.mli";	#reference MLI-1 resampled into geometry of MLI-2
  $diff_par_lt0 = $rslc_dir."/".$id."_lt0.diff_par";
  $diff_par_lt0_in = $diff_par_lt0.".in";
  $log = "$rslc_dir/".$id."_resamp_lt.log";   
  
  print "\n*** SLC #$k  ref. SLC: $ref_slc   SLC-2: $slc2   start time: $time ***\n";  
  print "log file: $log\n";
  print "initial MLI offset looks range: $rlks  azimuth: $azlks\n";
  print "resampled RSLC data directory: $rslc_dir\n";
  print "reference SLC: $ref_slc\n";
  print "reference SLC parameters: $ref_par\n";
  print "\nSLC-2: $slc2\n";
  print "SLC-2 parameter file: $slc2_par\n";
  print "SLC-2 range samples:  $width2[1]  azimuth lines: $lines2[1]\n";
  print "\nMLI-2: $mli2\n"; 
  print "MLI-2 parameter file: $mli2_par\n";
  print "MLI-2 range samples:  $mli2_width[1]\n";
  print "\nlookup table refinement DIFF_par: $diff_par_lt0\n";
  print "file with inputs to create_diff_par: $diff_par_lt0_in\n";
  print "reference MLI image resampled into geometry of MLI-2: $mli1_lt0\n";
  print "initial lookup table: $lt0\n";
  print "updated lookup table: $lt1\n";
  print "SLC offset parameter file: $off\n";
  
  open(LOG,">>$log") or die "ERROR $0: cannot open SLC_interp_lt_all log file: $log\n";
  print LOG "SLC_resamp_lt_all log file: $log   mode: $mode\n";
  print LOG "initial MLI offset looks range: $rlks   azimuth: $azlks\n";
  print LOG "resampled RSLC data directory: $rslc_dir\n";
  print LOG "reference SLC: $ref_slc\n";
  print LOG "reference SLC parameters: $ref_par\n";
  print LOG "reference MLI: $ref_MLI\n";
  print LOG "reference MLI parameters: $ref_MLI_par\n";

  print LOG "SLC-2: $slc2\n";
  print LOG "SLC-2 parameter file: $slc2_par\n";
  print LOG "SLC-2 range samples: $width2[1]   azimuth lines: $lines2[1]\n\n";
  print LOG "MLI-2: $mli2\n"; 
  print LOG "MLI-2 parameter file: $mli2_par\n\n";
  print LOG "MLI-2 range samples:  $mli2_width[1]\n";
  print LOG  "\nlookup table refinement DIFF_par: $diff_par_lt0\n";
  print LOG  "reference MLI image resampled into geometry of MLI-2: $mli1_lt0\n";
  print LOG  "initial lookup table: $lt0\n";
  print LOG  "updated lookup table: $lt1\n";
  print LOG  "SLC offset parameter file: $off\n";
  close LOG;

  if($mode == 0){
    print "\nmode 0: generate lookup table (MLI-2 into geometry of MLI-1) and resample MLI-1 image into the geometry of MLI-2\n";
    execute("rdc_trans $ref_MLI_par $dem_rdc $mli2_par $lt0", $log);

    if($mflg == 1){	#resample reference MLI image into the geometry of MLI-2
      execute("geocode $lt0 $ref_MLI $mli1_width[1] $mli1_lt0 $mli2_width[1] $mli2_lines[1] 0 0 - -", $log);
      execute("raspwr $mli1_lt0 $mli2_width[1] 1 0 1 1 $sc $exp", $log);
    }
  }

  if ($mode == 1){
    print "\nmode 1: refine lookup table based on measured offsets between MLI-1 resampled to the geometry of MLI-2\n"; 
    -e $mli1_lt0 or  die "\nERROR: missing resampled MLI-1 in MLI-2 geometry, generate these images running mode 0 with -m option\n";

    print "creating DIFF/GEO parameter file: $diff_par_lt0\n";
    if(-e $diff_par_lt0){
      print "deleting $diff_par_lt0\n";
      unlink $diff_par_lt0; #delete existing DIFF/GEO offset parameter file
    }                      
    open(DPAR, "> $diff_par_lt0_in") or die "ERROR $0: cannot create file with inputs to create_diff_par: $diff_par_lt0_in\n\n";
    print DPAR "$id\n0 0\n$nrpm $nazpm\n$rwinm $azwinm\n$thres_mli\n";
    close DPAR;

    execute("create_diff_par $mli2_par - $diff_par_lt0 1 < $diff_par_lt0_in", $log);
    print "\n";
    execute("init_offsetm $mli1_lt0 $mli2 $diff_par_lt0 $rlks $azlks $rpos $azpos - - $snr_min $patch", $log);
    execute("offset_pwrm $mli1_lt0 $mli2 $diff_par_lt0 $offs_lt0 $snr_lt0 - - - 2 - - - - 1", $log);
    execute("offset_fitm $offs_lt0 $snr_lt0 $diff_par_lt0 $coffs_lt0 - $thres_mli 3", $log);
    @rpolym =  extract_param($diff_par_lt0,"range_offset_polynomial:"); 
    @azpolym = extract_param($diff_par_lt0,"azimuth_offset_polynomial:");
    print "\nMLI offset polynomials:\n";
    print "@rpolym\n";
    print "@azpolym\n\n";
    execute("gc_map_fine $lt0 $mli1_width[1] $diff_par_lt0 $lt1", $log); 
  }

  if ($mode == 2){
    print "\nmode 2: resample SLC-2 to the geometry of the reference SLC using lookup table\n";
    if (-e $lt1) {
      execute("SLC_interp_lt $slc2 $ref_par1 $slc2_par $lt1 $ref_MLI_par $mli2_par - $rslc $rslc_par $blksz", $log);
    }
    else {
      print "NOTE: refined lookup table does not exist, using original lookup table: $lt0\n";
      execute("SLC_interp_lt $slc2 $ref_par1 $slc2_par $lt0 $ref_MLI_par $mli2_par - $rslc $rslc_par $blksz", $log);
    }
  }

  if ($mode == 3){
    print "\nmode 3: create offset parameter files for SLC resampling refinement, measure offsets, and calculate the SLC offset fit polynomials\n";
    if (-e $off) {
      print "deleting $off\n";
      unlink $off;
    }
    execute("create_offset $ref_par $rslc_par $off < create_offset.in",$log);
    print "\n";
    execute("offset_pwr $ref_slc $rslc $ref_par $rslc_par $off $offs $snr", $log);
    execute("offset_fit $offs $snr $off $coffs - - $npoly", $log);
    @rpoly =  extract_param($off,"range_offset_polynomial:"); 
    @azpoly = extract_param($off,"azimuth_offset_polynomial:");
    print "\nSLC offset polynomials:\n";
    print "@rpoly\n";
    print "@azpoly\n\n";
  }
  
  if($mode == 4){	#now apply refinement from offset parameter file    	
    print "\nmode 4: resample SLC using offset polynomials from SLC refinement\n";
    if (-e $lt1) {		
      execute("SLC_interp_lt $slc2 $ref_par $slc2_par $lt1 $mli1_par $mli2_par $off $rslc $rslc_par $blksz", $log);
    }
    else {
      execute("SLC_interp_lt $slc2 $ref_par $slc2_par $lt0 $mli1_par $mli2_par $off $rslc $rslc_par $blksz", $log);
    }
    $off2 = "$rslc_dir/$id"."_2.off";
    $offs2 = "$rslc_dir/$id"."_2.offs";		#binary offsets
    $coffs2 = "$rslc_dir/$id"."_2.coffs";	#culled offsets
    $snr2 = "$rslc_dir/$id"."_2.snr";
    print RSLC_TAB "$rslc  $rslc_par\n";	#output RSLC_tab record

    execute("create_offset $ref_par $rslc_par $off2 < create_offset.in",$log);
    printf("\n");
    execute("offset_pwr $ref_slc $rslc $ref_par $rslc_par $off2 $offs2 $snr2", $log);
    execute("offset_fit $offs2 $snr2 $off2 $coffs2 - - $npoly", $log);
    @rpoly =  extract_param($off,"range_offset_polynomial:"); 
    @azpoly = extract_param($off,"azimuth_offset_polynomial:");

    @rpoly2 =  extract_param($off2,"range_offset_polynomial:"); 
    @azpoly2 = extract_param($off2,"azimuth_offset_polynomial:");  

    printf "\nRSLC residual offset polynomials:\n";
    print "@rpoly2\n";
    print "@azpoly2\n\n";
    
    open(LOG,">>$log") or die "ERROR $0: cannot open SLC_interp_lt_all log file: $log\n";
    LOG->autoflush;      printf LOG "residual offset polynomials 1:\n";
    print LOG "\n@rpoly2\n";
    print LOG "@azpoly2\n\n";
    close LOG;

    if($rflag == 1){
      for($j = 1; $j <= 6; $j += 1){
        $rpoly3[$j] = $rpoly[$j] + $rpoly2[$j];
        $azpoly3[$j] = $azpoly[$j] + $azpoly2[$j];
      }
      $sv1 = sprintf "%.5f %12.5e %12.5e %12.5e %12.5e %12.5e",$rpoly3[1], $rpoly3[2], $rpoly3[3], $rpoly3[4]. $rpoly3[5],  $rpoly3[6],; 
      $sv2 = sprintf "%.5f %12.5e %12.5e %12.5e %12.5e %12.5e",$azpoly3[1], $azpoly3[2], $azpoly3[3], $azpoly3[4], $azpoly3[5], $azpoly3[6]; 

      execute("set_value $off $off \"range_offset_polynomial\"  \"$sv1\"", $log); 
      execute("set_value $off $off \"azimuth_offset_polynomial\" \"$sv2\"", $log);

#resample again after offset polynomial refinement and measure residual offsets
      execute("SLC_interp_lt $slc2 $ref_par1 $slc2_par $lt1 $mli1_par $mli2_par $off $rslc $rslc_par $blksz", $log);
      execute("offset_pwr $ref_slc $rslc $ref_par $rslc_par $off2 $offs2 $snr2", $log);
      execute("offset_fit $offs2 $snr2 $off2 $coffs2 - - $npoly", $log);  

      @rpoly2 = extract_param($off2,"range_offset_polynomial:"); 
      @azpoly2 = extract_param($off2,"azimuth_offset_polynomial:");  
      printf "\nResidual offset polynomials 2:\n";
      print "\n@rpoly2\n";
      print "@azpoly2\n\n";
      
      open(LOG,">>$log") or die "ERROR $0: cannot open SLC_interp_lt_all log file: $log\n";
      LOG->autoflush;
      printf LOG "residual offset polynomials 2:\n";
      print LOG "\n@rpoly2\n";
      print LOG "@azpoly2\n\n";
      close LOG;
      print "\n";
    }
  }
  
  $time = localtime;
  open(LOG,">>${log}") or die "\nERROR $0: cannot open log file: $log\n";
  print LOG "*** ref. SLC: $ref_slc   SLC-2: $slc2  END: $time ***\n";
  close LOG;
  print "*** ref. SLC: $ref_slc	SLC-2: $slc2  END: $time ***\n";       
}  

$time = localtime;
$log = "$rslc_dir/SLC_resamp_lt_all"."_$mode".".log"; 
open(LOG,">>${log}") or die "\nERROR $0: cannot open log file: $log\n";
print "\n*** $0 mode: $mode COMPLETED: $time ***\n";
print LOG "\n*** $0 mode: $mode COMPLETED: $time ***\n\n";
close LOG;
exit 0;

sub execute{
  my ($command, $log) = @_;  
  if (-e $log){open(LOG,">>$log") or die "\nERROR $0: cannot open log file: $log\n";}
  else {open(LOG,">$log") or die "\nERROR $0: cannot open log file: $log\n";} 
  LOG->autoflush; 
  print "$command\n";
  print LOG ("\n${command}\n");
  close LOG;
  $exit = system("$command 1>> $log");
  $exit == 0 or die "ERROR $0: non-zero exit status: $command\n"
}

sub extract_param{
  my ($infile,$keyword) = @_;
  open(PAR_IN,$infile) || die "\nERROR extract_param: cannot open parameter file: $infile\n";
  while(<PAR_IN>){
    chomp;
    @tokens = split;
    if($tokens[0] eq $keyword){close PAR_IN; return @tokens;}
  }
  close PAR_IN;
  die "\nERROR $0: keyword $keyword not found in file: $infile\n";
}