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package Geo::USCensus::TIGERweb;
use strict;
use warnings;
use LWP::UserAgent;
use HTTP::Request::Common;
use JSON::MaybeXS;
use IO::Socket::SSL;
use List::Util qw(first);
use Geo::USCensus::TIGERweb::Service;
=head1 NAME
Geo::USCensus::TIGERweb - The U.S. Census Bureau TIGER data services
=cut
our $VERSION = '0.01';
our $DEBUG = 0;
=head1 SYNOPSIS
use Geo::USCensus::TIGERweb;
print Dumper(Geo::USCensus::TIGERweb->info); # enumerates services
my $service = Geo::USCensus::TIGERweb->service('Tracts_Blocks');
print Dumper($service->info);
my $layer = $service->layer('Census Blocks'); # id or name
print Dumper($layer->info);
my $result = $layer->query(
# required fields
geometry => { x => -121.48778, y => 38.578793 }, # see below
fields => [ 'OID', 'GEOID', 'STATE', 'COUNTY' ],
# optional
# spatialRel => 'esriSpatialRelIntersects', # see below
# inSR => 4326, # the default, GPS coords
# outSR => 4326,
);
# convenience method: given a longitude and latitude, return
# the census block containing that point, or dies on error
my $blocknum = Geo::USCensus::TIGERweb->census_block_at_point(
lat => 38.578793,
lon => -121.48778
);
=head1 CLASS METHODS
=over 4
=item info
Returns a description of the available services.
=item service NAME
Constructor; returns a L<Geo::USCensus::TIGERweb::Service> handle to the
named service.
=cut
my $ua = LWP::UserAgent->new(ssl_opts => { verify_hostname => 0, SSL_verify_mode => IO::Socket::SSL::SSL_VERIFY_NONE });
my $url = 'https://tigerweb.geo.census.gov/arcgis/rest/services';
our $GLOBAL = bless { debug => 0, info => undef, path => 'TIGERweb' };
# in principle this could be turned into a general ArcGIS client
sub request {
my ($self, $path, $params) = @_;
$self = $GLOBAL if !ref($self);
my $full_path = join('/', $url, $self->{path});
$full_path .= "/$path" if $path;
$params = [ %$params ] if ref($params) eq 'HASH';
push @$params, ( f => 'pjson' ); # always use this
warn "POST $full_path\n" if $self->{debug};
warn encode_json($params)."\n" if $self->{debug} > 1;
my $response = $ua->request(
POST $full_path, Content => $params
);
if ( !$response->is_success ) {
$self->{error} = $response->status_line;
return;
}
my $data = decode_json($response->decoded_content);
if ( $data->{error} ) {
$self->{error} = $data->{error}{message};
return;
}
return $data;
}
sub info {
my $self = shift;
$self = $GLOBAL if !ref($self);
return $self->{info} ||= $self->request('');
}
sub create {
# internal constructor
my $self = shift;
my $subclass = shift;
my $subpath = shift;
$self = $GLOBAL if !ref($self);
my $class = "Geo::USCensus::TIGERweb::$subclass";
my $new = { debug => $self->{debug},
info => undef,
path => $self->{path} . '/' . $subpath,
};
bless $new, $class;
return $new;
}
sub service {
my $class = shift;
my $service_name = shift;
my $def = first { $_->{name} eq "TIGERweb/$service_name" }
@{ $GLOBAL->info->{services} };
die "TIGERweb service name '$service_name' not found" if !$def;
my $type = $def->{type};
return $GLOBAL->create('Service', "$service_name/$type");
}
=item census_block_at_point PARAMS
Takes numeric values for "lat" and "lon" and returns the census block number
at that location. This is actually the reason for this entire library.
=cut
sub census_block_at_point {
my ($class, %opt) = @_;
die "latitude and longitude required\n"
unless defined($opt{lat}) and defined($opt{lon});
$GLOBAL->{debug} = $opt{debug} if $opt{debug};
my $layer = $class->service('Tracts_Blocks')->layer('Census Blocks');
my $result = $layer->query(
geometry => { x => $opt{lon}, y => $opt{lat} },
fields => [ 'GEOID' ],
);
if ($layer->{error}) {
warn $layer->{error}."\n";
}
if (my $f = $result->{features}) {
if (scalar(@$f) == 0) {
warn "no census block found\n";
return;
} else {
return $f->[0]->{attributes}{GEOID};
}
} else {
warn "no features in query result\n";
return;
}
}
=back
=head1 LICENSE AND COPYRIGHT
Copyright (C) 2016 Mark Wells.
Copyright (C) 2016 Freeside Internet Services, Inc.
This program is free software; you can redistribute it and/or modify it
under the terms of either: the GNU General Public License as published
by the Free Software Foundation; or the Artistic License.
See http://dev.perl.org/licenses/ for more information.
=cut
1;
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