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lib/Geo/Raster/Image.pm  view on Meta::CPAN

# @brief Thin lines in the raster.
#
# This is an implementation of the algorithm in Jang, B-K., Chin,
# R.T. 1990. Analysis of Thinning Algorithms Using Mathematical
# Morphology. IEEE Trans. Pattern Analysis and Machine
# Intelligence. 12(6). 541-551. (Same as in GRASS but done in a bit
# different, and more generic way, I believe). 
#
# The thinning algorithm defines a set of structuring templates and
# applies them in several passes until there are no matches or until the
# maxiterations is reached. Trimming means certain structuring templates
# are applied to kill emerging short limbs which appear because of the
# noise in the raster.
# 
# Exple of thinning:
# @code
# $thinned_img = $img->thin(%options);
# @endcode
# or
# @code
# $img->thin(%options);
# @endcode
#
# @param[in] opt Includes as named parameters:
# - <I>algorithm</I> => character (optional). By default "B", the other option 
# is "A".
# - <I>trimming</I> => binary (optional). By default 0, the other option is 1. 
# Trimming removes artificial branches which grow on the side of wide lines in 
# thinnning, but it also shortens a bit the real branches.
# - <I>maxiterations</I> => integer (optional). By default 0 (no maximum, will 
# iterate until no cells are deleted).
# - <I>width</I> => double (optional). Used to define the maximum iterations 
# count. In case the width is given then the maxiterations is set to 
# int(width/2).
# @return a new raster. In void context changes this raster.
# @note The thinned raster must be a binary raster.
sub thin {
    my($self, %opt) = @_;
    $self = Geo::Raster->new($self) if defined wantarray;
    my @D1 = (+0,+0,-1,
	      +0,+1,+1,
	      -1,+1,-1);
    my @D2 = (-1,+0,+0,

lib/Geo/Raster/Image.pm  view on Meta::CPAN

	      +1,+1,+0,
	      -1,+0,+0);
    my @G8 = (+1,+0,+0,
	      +0,+1,+0,
	      +0,+0,+0);
    my @trimmer = (\@G1,\@G2,\@G3,\@G4,\@G5,\@G6,\@G7,\@G8);
    my $algorithm = $opt{algorithm};
    $algorithm = 'B' unless $algorithm;
    my $trimming = $opt{trimming};
    $trimming = 0 unless $trimming;
    my $maxiterations = $opt{maxiterations};
    $maxiterations = 0 unless $maxiterations;
    my $width = $opt{width};
    $maxiterations = int($width/2) if $width;
    my @thinner;
    if ($algorithm eq 'B') {
	if ($trimming) {
	    @thinner = (\@D1,\@D2,\@E1,@trimmer,
			\@D2,\@D3,\@E2,@trimmer,
			\@D3,\@D4,\@E3,@trimmer,
			\@D4,\@D1,\@E4,@trimmer);
	} else {
	    @thinner = (\@D1, \@D2, \@E1, \@D2, \@D3, \@E2,
			\@D3, \@D4, \@E3, \@D4, \@D1, \@E4);

lib/Geo/Raster/Image.pm  view on Meta::CPAN

    } else {
	croak "thin: $algorithm: unknown algorithm";
    }
    my ($m, $M, $i) = (0,0,1);
    do {
	$M = $m;
	foreach (@thinner) {
	    $m += ral_grid_applytempl($self->{GRID}, $_, 0);
	    print STDERR "#" unless $opt{quiet};
	}
	print STDERR " thinning, pass $i/$maxiterations: deleted ", $m-$M, " cells\n" unless $opt{quiet};
	$i++;
    } while ($m > $M and !($maxiterations > 0 and $i > $maxiterations));
    return $self if defined wantarray;
}

## @method Geo::Raster borders(%params)
#
# @brief Borders between zones.
# 
# This method returns a binary raster, where the borders have the
# value of 1.
#