$ ./6.am.pl 
Subroutine get_logger redefined at ./6.am.pl line 134.
INFO: ./6.am.pl
INFO: pi is 3.14159265358979 
INFO: Bonneville max altitude in feet: 5200
Error fetching: 500 Server closed connection without sending any data back at ./6.am.pl line 298.
$ 

##</code><code>##

sub get_open_elevation {
  my ( $lat, $lon, $debug ) = @_;

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

  $debug //= 0;

  #my $ua = LWP::UserAgent->new( 'send_te' => '0' );
  my $ua = LWP::UserAgent->new( agent =>
      'Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Firefox/78.0', );
  my $r = HTTP::Request->new(
    'GET' =>
'https://api.open-elevation.com/api/v1/lookup?locations=$lat%2C$lon',
    [
      'Accept'     => '*/*',
      'User-Agent' => 'curl/7.55.1'
    ],

  );
  my $response = $ua->request( $r, );

  if ( $debug > 0 ) {

    $logger->debug("$0 : verbose");
  }

  die "Error fetching: " . $response->status_line
    unless $response->is_success;

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

  return 5000;

}

##</code><code>##


#!/usr/bin/perl 

use v5.028;    # strictness implied
use warnings;
use feature qw[ signatures ];
no warnings qw[ experimental::signatures ];

use DateTime;
use DateTime::Format::ISO8601;
use DateTime::TimeZone;
use Log::Log4perl;
use Try::Tiny;

our $debug = 0;

my $logger     = init_log();
my $ref_events = init_event();

my $date_str = "2021-10-14";
my $time_str = "03:22:31";

@{$_}{qw(date time)} = ( $date_str, $time_str ) for @$ref_events;
my @events = @$ref_events;

my $pi = atan2( 1, 1 ) * 4;
$logger->info("pi is $pi ");
my $redrock = 5200;    #Willsey thumbnail for Bonneville Trail elevation
$logger->info("Bonneville max altitude in feet: $redrock");

## event loop

# Initial previous event to something
my ( $prev_lat, $prev_long ) =
  ( -112, 42 );        #some point in the snake river plain

for my $event (@events) {
  my $epoch = parse_event($event);

### determine altitude withOUT google

  die unless exists $event->{location};    # restriction
  my $return = get_open_elevation( $event->{location}->{lat},
    $event->{location}->{lon}, $debug );
  $logger->info(
    " $event->{name} $event->{location}->{lat}  $event->{location}->{lon}");

  $logger->info("return from the google is $return meters");
  my $feet = 3.28084 * $return;
  $logger->info("Altitude in feet is $feet");
  my $diff = $redrock - $feet;
  $logger->info("Difference from max Bonneville elevation is $diff ft");

### Elevation with USGS

  use Geo::WebService::Elevation::USGS;

  my $eq = Geo::WebService::Elevation::USGS->new();
  my $alt =
    $eq->elevation( $event->{location}->{lat}, $event->{location}->{lon} )
    ->{Elevation};

  $logger->info("USGS elevation is $alt ft");

### compare values

  my $percent = percent_error( $feet, $alt );
  $logger->info("Percent difference is $percent");



### distance with GPS::Point
  use GPS::Point;
  my $gps = GPS::Point->new( lat => $prev_lat, lon => $prev_long );
  my $dist =
    $gps->distance( $event->{location}->{lat}, $event->{location}->{lon} );
  my $feet2 = 3.28084 * $dist;
  my $miles = $feet2 / 5280;

  #$logger->info("distance is $feet2 feet");
  $logger->info("distance is $miles miles");



### rotate values
  $prev_lat  = $event->{location}->{lat};
  $prev_long = $event->{location}->{lon};
  $logger->info("==============");
}
## end event loop

#### end main
sub init_event {

  # define unique event records as anonymous hash refs.
  # thx anomalous monk
  my $ar_events = [
    {
      "name"     => "Boise",
      "location" => { lon => -116.2, lat => 43.61 },
    },
    {
      "name"     => "near sublett",
      "location" => { lon => -113.2104084, lat => 42.3278114 },
    },
    {
      "name"     => "snowville",
      "location" => { lon => -112.7105234, lat => 41.9655701 },
    },
    {
      "name"     => "juniper",
      "location" => { lon => -112.9842191, lat => 42.152429 },
    },

    # and so on...
  ];

  return $ar_events;

}

sub percent_error {
  my ( $val1, $val2 ) = @_;

  my $diff    = abs( $val2 - $val1 );
  my $median  = ( $val1 + $val2 ) / 2.0;
  my $percent = $diff * 100 / $median;
  return ($percent);
}

sub init_log {
  {

    package Log::Log4perl;
    sub get_logger ($pkg) { return bless [], $pkg; }

    sub show (@arg) { warn @arg, "\n"; }
    sub debug ( $ignore, @rest ) { show( 'DEBUG: ', @rest ); }
    sub info ( $ignore, @rest ) { show( 'INFO: ', @rest ); }
    sub warn ( $ignore, @rest ) { show( 'WARNING: ', @rest ); }

    sub error ( $ignore, @rest ) { die 'ERROR: ', @rest, "\n"; }
  }

  my $logger2 = Log::Log4perl->get_logger();
  $logger2->info("$0");
  return $logger2;
}

sub event2str {
  my $event = shift;

  if ( !exists $event->{_is_parsed} ) {
    warn "event has not been parsed, just dumping it...";
    print Dump($event);
  }
  my $str =
      $event->{name} . " on "
    . $event->{datetime} . " ("
    . $event->{datetime}->epoch
    . " seconds unix-epoch)"
    . " timezone: "
    . $event->{datetime}->time_zone->name;
  if ( exists $event->{location} ) {
    if ( ref( $event->{location} ) eq 'HASH' ) {
      $str .=
          " (lat: "
        . $event->{location}->{lat}
        . ", lon: "
        . $event->{location}->{lon} . ")";
    }
    else { $str .= "(" . $event->{location} . ")" }
  }
  return $str;
}

sub parse_event {
  my $event = shift;

  $debug //= 0;
  if ( !exists $event->{date} ) { die "date field is missing from event." }

  my $datestr = $event->{date};

  die "event does not have a 'name' field, please specify one, anything really."
    unless exists $event->{name};

  my $timestr = "00:00:01";
  if ( exists $event->{time} ) {
    $timestr = $event->{time};
    print "event2epoch(): setting time to '$timestr' ...\n"
      if $debug > 0;
    die "time '$timestr' is not valid, it must be in the form 'hh:mm:ss'."
      unless $timestr =~ /^\d{2}:\d{2}:\d{2}$/;
  }
  else { $event->{time} = $timestr }

  my $isostr = $datestr . 'T' . $timestr;
  my $dt     = DateTime::Format::ISO8601->parse_datetime($isostr);
  die "failed to parse date '$isostr', check date and time fields."
    unless defined $dt;
  $event->{datetime} = $dt;

  my $tzstr = 'UTC';
  if ( exists $event->{timezone} ) {
    $tzstr = $event->{timezone};
    print
"event2epoch(): found a timezone via 'timezone' field as '$tzstr' (that does not mean it is valid) ...\n"
      if $debug > 0;
  }
  elsif ( exists $event->{location} ) {
    my $loc = $event->{location};
    if ( ( ref($loc) eq '' ) && ( $loc =~ /^[a-zA-Z]$/ ) ) {

      # we have a location string
      my @alltzs = DateTime::TimeZone->all_names;
      my $tzstr;
      for (@alltzs) {
        if ( $_ =~ /$loc/i ) { $tzstr = $_; last }
      }
      die
"event's location can not be converted to a timezone, consider specifying the 'timezone' directly or setting 'location' coordinates with: \[lat,lon\]."
        unless $tzstr;
      print
"event2epoch(): setting timezone via 'location' name to '$timestr' ...\n"
        if $debug > 0;
    }
    elsif ( ( ref($loc) eq 'HASH' )
      && ( exists $loc->{lat} )
      && ( exists $loc->{lon} ) )
    {
      # we have a [lat,lon] array for location
      require Geo::Location::TimeZone;
      my $gltzobj = Geo::Location::TimeZone->new();
      $tzstr = $gltzobj->lookup( lat => $loc->{lat}, lon => $loc->{lon} );
      if ( !$tzstr ) {
        die "timezone lookup from location coordinates lat:"
          . $loc->{lat}
          . ", lon:"
          . $loc->{lon}
          . " has failed.";
      }
      print "event2epoch(): setting timezone via 'location' coordinates lat:"
        . $loc->{lat}
        . ", lon:"
        . $loc->{lon}
        . " ...\n"
        if $debug > 0;
    }
  }
  if ($tzstr) {
    print "event2epoch(): deduced timezone to '$tzstr' and setting it ...\n"
      if $debug > 0;
    try {
      $dt->set_time_zone($tzstr)
    }
    catch {
      die "$_\n failed to set the timezone '$tzstr', is it valid?"
    }
  }

  $event->{_is_parsed} = 1;
  $event->{epoch}      = $dt->epoch;
  return $event->{epoch};
}





sub get_open_elevation {
  my ( $lat, $lon, $debug ) = @_;

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

  $debug //= 0;

  #my $ua = LWP::UserAgent->new( 'send_te' => '0' );
  my $ua = LWP::UserAgent->new( agent =>
      'Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Firefox/78.0', );
  my $r = HTTP::Request->new(
    'GET' =>
'https://api.open-elevation.com/api/v1/lookup?locations=$lat%2C$lon',
    [
      'Accept'     => '*/*',
      'User-Agent' => 'curl/7.55.1'
    ],

  );
  my $response = $ua->request( $r, );

  if ( $debug > 0 ) {

    $logger->debug("$0 : verbose");
  }

  die "Error fetching: " . $response->status_line
    unless $response->is_success;

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

  return 5000;

}

__END__