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=head1 NAME |
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Geo::LatLon2Place - convert latitude and longitude to nearest place |
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=head1 SYNOPSIS |
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use Geo::LatLon2Place; |
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my $db = Geo::LatLon2Place->new ("/var/lib/mydb.cdb"); |
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=head1 DESCRIPTION |
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This is a simple-purpose module that tries to do one job: find the nearest |
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placename for a point on earth. It doesn't claim to do a perfect job, but |
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it tries to be simple to set up, simple to use and be fast. |
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=head2 BUILDING AND SETTING UP |
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To build this module, you need tinycdb, a cdb implementation by Michael |
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Tokarev, or a compatible library. On GNU/Debian-based systems you can get |
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this by executing F<apt-get install libcdb-dev>. |
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After install the module, you need to generate a database using the |
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F<geo-latlon2place-makedb> command. |
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Currently, it accepts various databases from geonames |
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(L<https://www.geonames.org/export/>, note the license), for example, |
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F<cities500.zip>, which lists all places with population 500 or more: |
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wget https://download.geonames.org/export/dump/cities500.zip |
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unzip cities500.zip |
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geo-latlon2place-makedb --geonames-gazetteer cities500.txt ll2place.cdb |
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This will create a file F<ll2place.cdb> that you can use for lookups |
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with this module. At the time of this writing, the F<cities500> database |
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results in about a 10MB file while the F<allCountries> database results in |
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about 120MB. |
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=over 4 |
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=cut |
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package Geo::LatLon2Place; |
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use common::sense; |
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use Carp (); |
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BEGIN { |
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our $VERSION = 0.01; |
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require XSLoader; |
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XSLoader::load __PACKAGE__, $VERSION; |
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eval 'sub TORAD() { ' . ((atan2 1,0) / 180) . ' }'; |
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} |
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sub new { |
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my ($class, $path) = @_; |
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open my $fh, "<", $path |
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or Carp::croak "$path: $!\n"; |
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my $self = bless [$fh, ""], $class; |
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cdb_init $self->[1], fileno $self->[0] |
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and Carp::croak "$path: unable to open as cdb file\n"; |
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(my ($magic, $version), $self->[2], $self->[3]) = unpack "a4VVV", cdb_get $self->[1], ""; |
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$magic eq "SRGL" |
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or Carp::croak "$path: not a Geo::LatLon2Place file"; |
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$version == 1 |
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or Carp::croak "$path: version mismatch (got $version, expected 1)"; |
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$self |
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} |
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sub DESTROY { |
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my ($self) = @_; |
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cdb_free $self->[1]; |
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} |
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sub lookup { |
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my ($self, $lat, $lon, $radius) = @_; |
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$radius ||= $self->[2]; |
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$radius = int +($radius + $self->[2] - 1) / $self->[2]; |
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my $coslat = cos abs $lat * TORAD; |
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my $blat = int $self->[3] * $coslat; |
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my $cx = int (($lon + 180) * $blat / 360); |
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my $cy = int (($lat + 90) * $self->[3] / 180); |
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my ($min, $res) = (1e00); |
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for my $y ($cy - $radius .. $cy + $radius) { |
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for my $x ($cx - $radius .. $cx + $radius) { |
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for (unpack "(C/a*)*", cdb_get $self->[1], pack "s< s<", $x, $y) { |
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my ($plat, $plon, $w, $data) = unpack "s< s< C a*"; |
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$plat = $plat * ( 90 / 32767); |
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$plon = $plon * (180 / 32767); |
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my $dx = ($lon - $plon) * TORAD * $coslat; |
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my $dy = ($lat - $plat) * TORAD; |
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my $d2 = ($dx * $dx + $dy * $dy) * $w; |
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$d2 >= $min |
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or ($min, $res) = ($d2, $data); |
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} |
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} |
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} |
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$res |
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} |
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=head1 AUTHOR |
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Marc Lehmann <schmorp@schmorp.de> |
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http://home.schmorp.de/ |
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=cut |
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