use LWP::UserAgent;
  use HTTP::Request;
  use Data::Roundtrip;

...
  my $req = HTTP::Request->new(
...

  $response = $ua->request($req);
  die "Error fetching: " . $response->status_line
    unless $response->is_success;

  my $content = $response->decoded_content;
  my $data    = Data::Roundtrip::json2perl($content);
  die "failed to parse received data:\n$content\n"
    unless exists $data->{'elevation'};

  return $data->{'elevation'};