File Coverage

blib/lib/Geo/AnomalyDetector.pm

Criterion	Covered	Total	%
statement	44	44	100.0
branch	11	14	78.5
condition	4	10	40.0
subroutine	6	6	100.0
pod	0	2	0.0
total	65	76	85.5

package Geo::AnomalyDetector;

use strict;
use warnings;

use Statistics::Basic qw(mean stddev);
use Math::Trig;
# use Geo::Inverse;

=head1 NAME

Geo::AnomalyDetector - Detect anomalies in geospatial coordinate datasets

=head1 SYNOPSIS

This module analyzes latitude and longitude data points to identify anomalies based on their distance from the mean location.

  use Geo::AnomalyDetector;

  my $detector = Geo::AnomalyDetector->new(threshold => 3);
  my $coords = [ [37.7749, -122.4194], [40.7128, -74.0060], [35.6895, 139.6917] ];
  my $anomalies = $detector->detect_anomalies($coords);
  print "Anomalies: " . join ", ", map { "($_->[0], $_->[1])" } @{$anomalies};

Each co-ordinate can be either a two element array of [latitude, longitude] or an object that has
C and C methods.

=head1	VERSION

0.02

=cut

our $VERSION = '0.02';

sub new {
	my ($class, %args) = @_;
	my $self = {
		threshold => $args{threshold} || 3,
		unit => $args{unit} || 'K',
	};
	bless $self, $class;
	return $self;
}

sub detect_anomalies {
	my ($self, $coordinates) = @_;

	my @distances;
	my $mean_lat = mean(map { (ref($_) eq 'ARRAY') ? $_->[0] : $_->latitude() } @{$coordinates});
	my $mean_lon = mean(map { (ref($_) eq 'ARRAY') ? $_->[1] : $_->longitude() } @{$coordinates});

	# my $inverse = Geo::Inverse->new();

	die if(!defined($mean_lat) || !defined($mean_lon));

	foreach my $coord (@{$coordinates}) {
		my ($lat, $lon) = (ref($coord) eq 'ARRAY') ? @{$coord} : ($coord->latitude(), $coord->longitude());
		die if(!defined($lat) || !defined($lon));
		# my $distance = distance($lat, $lon, $mean_lat, $mean_lon, 'K');

		# Thanks to Robbie Hatley for working out the arguments to Math::Trig
		my $t1 = $lon * (pi/180);
		my $p1 = (pi/2) - ($lat * (pi/180));
		my $t2 = $mean_lon * (pi/180);
		my $p2 = (pi/2) - ($mean_lat * (pi/180));
		my $rho = ($self->{'unit'} eq 'M') ? 3959.0 : 6371.0;	# radius of Earth in miles/Km
		my $distance = Math::Trig::great_circle_distance($t1, $p1, $t2, $p2, $rho);
		push @distances, $distance;
	}

	my $mean_dist = mean(@distances);
	my $std_dist = stddev(@distances);

	my @anomalies;
	for my $i (0 .. $#distances) {
		if (abs($distances[$i] - $mean_dist) > ($self->{threshold} * $std_dist)) {
			push @anomalies, $coordinates->[$i];
		}
	}

	return \@anomalies;
}

# Now use Math::Trig.  I tried Geo::Inverse, but that always throws messages about undefined variables

# =head2 distance
#
# Calculate the distance between two geographical points using latitude and longitude.
# Supports distance in kilometres (K), nautical miles (N), or miles.
#
# From L
# FIXME:  use Math::Trig
#
# =cut
#
# sub distance {
	# my ($lat1, $lon1, $lat2, $lon2, $unit) = @_;
	# my $theta = $lon1 - $lon2;
	# my $dist = sin(_deg2rad($lat1)) * sin(_deg2rad($lat2)) + cos(_deg2rad($lat1)) * cos(_deg2rad($lat2)) * cos(_deg2rad($theta));
	# $dist = _acos($dist);
	# $dist = _rad2deg($dist);
	# $dist = $dist * 60 * 1.1515;
	# if ($unit eq 'K') {
		# $dist = $dist * 1.609344;	# number of kilometres in a mile
	# } elsif ($unit eq 'N') {
		# $dist = $dist * 0.8684;
	# }
	# return ($dist);
# }
#
# my $pi = atan2(1,1) * 4;
#
# #::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
# #:::  This function get the arccos function using arctan function   :::
# #::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
# sub _acos {
	# my ($rad) = @_;
	# my $ret = atan2(sqrt(1 - $rad**2), $rad);
	# return $ret;
# }
#
# #::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
# #:::  This function converts decimal degrees to radians			 :::
# #::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
# sub _deg2rad {
	# my ($deg) = @_;
	# return ($deg * $pi / 180);
# }
#
# #::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
# #:::  This function converts radians to decimal degrees			 :::
# #::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
# sub _rad2deg {
	# my ($rad) = @_;
	# return ($rad * 180 / $pi);
# }

=head1 AUTHOR

Nigel Horne, C<<  >>

=head1 BUGS

=head1 SEE ALSO

=over 4

=item * L

=item * L

=back

=head1 SUPPORT

This module is provided as-is without any warranty.

Please report any bugs or feature requests to C,
or through the web interface at
L.
I will be notified, and then you'll
automatically be notified of progress on your bug as I make changes.

You can find documentation for this module with the perldoc command.

    perldoc Geo::AnomalyDetector

You can also look for information at:

=over 4

=item * MetaCPAN

L

=item * RT: CPAN's request tracker

L

=item * CPAN Testers' Matrix

L

=item * CPAN Testers Dependencies

L

=back

=head1 LICENSE AND COPYRIGHT

Copyright 2025 Nigel Horne.

This program is released under the following licence: GPL2

=cut

1;

__END__