use 5.34.0;
use Feature::Compat::Class;
#================================================================================
class NearestTown; # uses data from GeoNames.org - generated by merge_geonames.pl
#================================================================================
use Data::Printer;
use IO::All -utf8; # for file handling
use POSIX qw(round);
use List::Util 'uniq';
use Math::Trig qw(great_circle_distance deg2rad);
# ---------------------------
# CONFIG
# ---------------------------
my $cities_file = 'cities_full.txt'; # output from merge_geonames.pl
my $oceans_file = 'hydro_features.txt'; # from GeoNames.org
my $min_population = 5000; # ignore tiny settlements
my $search_radius = 1.0; # degrees for bounding box
# ---------------------------
# Load cities into memory
# ---------------------------
field $cities = do {
my @csrc = io($cities_file)->chomp->slurp;
my @cities;
for (@csrc) {
# 51.24389 -1.26154 Overton Hampshire England United Kingdom GB 3392
my ($lat,$lon,$name,$admin1,$admin2,$cname,$cc,$pop) = split /\t/;
next unless $pop =~ /^\d+$/ && $pop >= $min_population; # will skip header row
push @cities, {
name => $name, # city/town name
lat => $lat + 0, # ensure numeric
lon => $lon + 0, # ensure numeric
cc => $cc, # abbreviated country code [GB, ES, US etc]
country => $cname,
admin1 => $admin1, # state/province
admin2 => $admin2, # not useful
pop => $pop + 0, # ensure numeric
};
} # p @cities
\@cities;
};
# -----------------------------
# Load oceans/seas into memory
# -----------------------------
field $oceans = do {
my @src = io($oceans_file)->chomp->slurp;
my @hydro;
for (@src) {
next unless $_ =~ /^\d+/; # skip header row
my @f = split /\t/;
my ($name, $feat_code, $lat, $lon, $admin2) = @f[1,3,4,5,8];
push @hydro, {
name => $name,
lat => $lat,
lon => $lon,
code => $feat_code,
admin2 => $admin2,
};
}
\@hydro;
};
# ---------------------------
# Distance function (Haversine)
# ---------------------------
method haversine_km {
# convert degrees to radians
my ($lat1, $lon1, $lat2, $lon2) = map { deg2rad($_) } @_;
# compute great-circle distance, multiplying by 6371 converts radians → kilometres
# since 6371 km ≈ Earth’s mean radius.
return 6371 * great_circle_distance( $lon1, $lat1, $lon2, $lat2 );
}
# ---------------------------
# Nearest town lookup
# ---------------------------
method nearest_town ($lat, $lon) { # p $lat; p $lon;
# creates a latitude/longitude rectangle centered on your tile ($lat, $lon),
# extending $search_radius degrees in each direction. Example: if $lat = 60,
# $search_radius = 0.5, then the box covers 59.5–60.5°N.
my ($min_lat, $max_lat) = ($lat - $search_radius, $lat + $search_radius);
my ($min_lon, $max_lon) = ($lon - $search_radius, $lon + $search_radius);
# $best will hold the closest city record found.
# $min_dist starts at the maximum possible distance within the tile
my $tile_diagonal_km = 0.5 * sqrt( (111)**2 + (111 * cos(deg2rad($lat)))**2 );
my ($best, $min_distance) = (undef, $tile_diagonal_km);
for my $location (@$cities) {
# This is a fast bounding-box prefilter — saves time by ignoring cities too
# far away (no need to compute distance).
next if $location->{lat} < $min_lat || $location->{lat} > $max_lat;
next if $location->{lon} < $min_lon || $location->{lon} > $max_lon; # p $c->{lon};
# compute great-circle distance using centre of tile - lat + 0.5, lon + 0.5
my $distance = $self->haversine_km($lat + 0.5, $lon + 0.5,
$location->{lat}, $location->{lon});
# printf "Tile diagonal km: %.1f\n", $tile_diagonal_km;
# print what you think you used
# printf "Tile centre: %dN %dE\n", $lat + 0.5, $lon + 0.5;
# print city coordinates and the computed distance:
# printf "Candidate: %s (%s) at %.2f, %.2f -> dist=%.1f km\n",
# $c->{name}, $c->{country}, $c->{lat}, $c->{lon}, $d;
# If this city is closer than any previous one, store it as the current best match.
if ( $distance < $min_distance ) {
$best = $location; $min_distance = $distance;
}
}
# say "No nearby city found for $lat / $lon" unless $best;
if ($best) {
my $formatted_info = $self->format_city_info($best, $min_distance);
return $formatted_info;
}
else {
if ( my $ocean_tile = $self->is_ocean_tile($lat, $lon) ) {
return $ocean_tile;
}
}
return 0; # can't find anything
}
method format_city_info ($city, $distance) {
my $location = join ', ', grep { $_ } uniq( @{$city}{ qw/name admin1 admin2 country/ } ); # not using cc
return sprintf '%s [%s km from tile center]', $location, round($distance);
}
method is_ocean_tile ($lat, $lon) {
for my $threshold_km (50, 100, 200, 500) { # increase search radius to avoid 'no data'
for my $o (@$oceans) {
my $distance = $self->haversine_km($lat, $lon, $o->{lat}, $o->{lon});
if ( $distance < $threshold_km ) {
my $hydro_name = $o->{name};
# append sea / ocn / bay unless already contains it
$hydro_name .= ' ' . ucfirst lc $o->{code}
unless $hydro_name =~ /$o->{code}\Z/i;
return sprintf '%s, %s [ocean tile, %s km from tile centre]',
$hydro_name, $o->{admin2}, round($distance);
}
}
}
return 0; # can't find anything
}
1;
