File Coverage

blib/lib/Geo/WebService/Elevation/USGS.pm

Criterion	Covered	Total	%
statement	134	172	77.9
branch	41	88	46.5
condition	15	38	39.4
subroutine	28	33	84.8
pod	6	6	100.0
total	224	337	66.4

=head1 NAME

Geo::WebService::Elevation::USGS - Elevation queries against USGS web services.

=head1 SYNOPSIS

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

 my $eq = Geo::WebService::Elevation::USGS->new();
 print "The elevation of the White House is ",
   $eq->elevation( 38.898748, -77.037684 )->{Elevation},
   " feet above sea level.\n";

=head1 NOTICE

Some time while I was not looking the USGS changed the web address and
the API for the point elevation service yet again.

I have dealt with this by resurrecting the C attribute and
defaulting it to a true value. This attribute affects the hash returned
by the C method. See that method's documentation
for the gory details.

You are encouraged to set this attribute to a false value as soon as you
can, since my long-term plan is to discourage a true value, and then
ultimately deprecate and remove it.

=head1 DESCRIPTION

This module executes elevation queries against the United States
Geological Survey's Elevation Data Point Service. You provide the
latitude and longitude in degrees, with south latitude and west
longitude being negative. The return is typically a hash containing the
data you want. Query errors are exceptions by default, though the object
can be configured to signal an error by an undef response, with the
error retrievable from the 'error' attribute.

For documentation on the underlying web service, see
L,
particularly L.

For all methods, the input latitude and longitude are documented at the
above web site as being WGS84, which for practical purposes I understand
to be equivalent to NAD83. The vertical reference is not documented
under the above link, but correspondence with the USGS says that it is
derived from the National Elevation Dataset (NED; see
L).
This is referred to NAD83 (horizontal) and NAVD88 (vertical). NAVD88 is
based on geodetic leveling surveys, B
and takes as its zero datum sea level at Father Point/Rimouski, in
Quebec, Canada. Alaska is an exception, and is based on NAD27
(horizontal) and NAVD29 (vertical).

Anyone interested in the gory details may find the paper I
GPS Height into NAVD88 Elevation with the GEOID96 Geoid Height Model> by
Dennis G. Milbert, Ph.D. and Dru A. Smith, Ph.D helpful. This is
available at L. This
paper states that the difference between ellipsoid and geoid heights
ranges between -75 and +100 meters globally, and between -53 and -8
meters in "the conterminous United States."

=head2 Methods

The following public methods are provided:

=cut

package Geo::WebService::Elevation::USGS;

use 5.008;

use strict;
use warnings;

use Carp;
use HTTP::Request::Common;
use JSON;
use LWP::UserAgent;
use Scalar::Util 1.10 qw{ blessed looks_like_number };

our $VERSION = '0.201';

# use constant USGS_URL => 'https://ned.usgs.gov/epqs/pqs.php';
# use constant USGS_URL => 'https://nationalmap.gov/epqs/pqs.php';
use constant USGS_URL => 'https://epqs.nationalmap.gov/v1/json';

use constant ARRAY_REF	=> ref [];
use constant CODE_REF	=> ref sub {};
use constant HASH_REF	=> ref {};
use constant REGEXP_REF	=> ref qr{};

my $using_time_hires;
{
    my $mark;
    if ( eval {
	    require Time::HiRes;
	    Time::HiRes->can( 'time' ) && Time::HiRes->can( 'sleep' );
	} ) {
	*_time = \&Time::HiRes::time;
	*_sleep = \&Time::HiRes::sleep;
	$using_time_hires = 1;
    } else {
	*_time = sub { return time };
	*_sleep = sub { return sleep $_[0] };
    }

    $mark = _time();
    sub _pause {
##	my ( $self ) = @_;	# Invocant unused
	my $now = _time();
	while ( $now < $mark ) {
	    _sleep( $mark - $now );
	    $now = _time();
	}
	# We use __PACKAGE__ rather than $self because the attribute is
	# static, and it needs to be static because it needs to apply to
	# everything coming from this user, not just everything coming
	# from the invoking object.
	$mark = $now + __PACKAGE__->get( 'throttle' );
	return;
    }
}

=head3 $eq = Geo::WebService::Elevation::USGS->new();

This method instantiates a query object. If any arguments are given,
they are passed to the set() method. The instantiated object is
returned.

=cut

sub new {
    my ($class, @args) = @_;
    ref $class and $class = ref $class;
    $class or croak "No class name specified";
    shift;
    my $self = {
	carp	=> 0,
	compatible	=> 1,
	croak	=> 1,
	error	=> undef,
	places	=> undef,
	retry	=> 0,
	retry_hook => sub {},
	timeout	=> 30,
	trace	=> undef,
	units	=> 'FEET',
	usgs_url	=> $ENV{GEO_WEBSERVICE_ELEVATION_USGS_URL} || USGS_URL,
    };
    bless $self, $class;
    @args and $self->set(@args);
    return $self;
}

my %mutator = (
    croak	=> \&_set_literal,
    carp	=> \&_set_literal,
    compatible	=> \&_set_literal,
    error	=> \&_set_literal,
    places	=> \&_set_integer_or_undef,
    retry	=> \&_set_unsigned_integer,
    retry_hook	=> \&_set_hook,
    throttle	=> \&_set_throttle,
    timeout	=> \&_set_integer_or_undef,
    trace	=> \&_set_literal,
    units	=> \&_set_literal,
    usgs_url	=> \&_set_literal,
);

my %access_type = (
    throttle	=> \&_only_static_attr,
);

foreach my $name ( keys %mutator ) {
    exists $access_type{$name}
	or $access_type{$name} = \&_no_static_attr;
}

=head3 %values = $eq->attributes();

This method returns a list of the names and values of all attributes of
the object. If called in scalar context it returns a hash reference.

=cut

sub attributes {
    my $self = shift;
    my %attr;
    foreach (keys %mutator) {
	$attr{$_} = $self->{$_};
    }
    return wantarray ? %attr : \%attr;
}

=head3 $rslt = $usgs->elevation($lat, $lon, $valid);

This method queries the data base for the elevation at the given
latitude and longitude, returning the results as a hash reference.

If the C attribute is true, this hash will contain the
following keys:

=over

=item {Data_Source} => A text description of the data source (always 'USGS Elevation Point Query Service');

=item {Elevation} => The elevation in the given units;

=item {Units} => The units of the elevation (C<'Feet'> or C<'Meters'>);

=item {x} => The C<$lon> argument;

=item {y} => The C<$lat> argument.

=back

If the C attribute is false, the hash will contain the
values documented at L. B
that the elevation comes back in key C<{value}>. For my own sanity key
C<{Elevation}> is added to this hash; it contains the value of
C<{value}>, rounded to C if that attribute is set.

You can also pass a C, C, or C
object in lieu of the C<$lat> and C<$lon> arguments. If you do this,
C<$valid> becomes the second argument, rather than the third.

If the optional C<$valid> argument is specified as a true value B
the returned data are invalid, nothing is returned. The source does not
seem to produce data recognizable as invalid, so you will probably not
see this.

=cut

sub elevation {
    my ( $self, $lat, $lon, $valid ) = _latlon( @_ );
    my $retry_limit = $self->get( 'retry' );
    my $retry = 0;

    while ( $retry++ <= $retry_limit ) {

	$self->{error} = undef;

	$self->_pause();

	my $rslt;
	eval {
	    $rslt = $self->_request(
		x	=> $lon,
		y	=> $lat,
		units	=> $self->{units},
	    );
	    1;
	} or do {
	    $self->_error( $@ );
	    next;
	};

	$rslt
	    or next;

	not $valid
	    or is_valid( $rslt )
	    or next;

	return $rslt;

    } continue {

	if ( $retry <= $retry_limit ) {
	    ( my $sub = ( caller( 0 ) )[3] ) =~ s/ .* :: //smx;
	    $self->get( 'retry_hook' )->( $self, $retry, $sub, $lat,
		$lon );
	}

    }

    $self->{croak} and croak $self->{error};
    return;

}

=head3 $value = $eq->get($attribute);

This method returns the value of the given attribute. It will croak if
the attribute does not exist.

=cut

sub get {
    my ($self, $name) = @_;
    $access_type{$name}
	or croak "No such attribute as '$name'";
    my $holder = $access_type{$name}->( $self, $name );
    return $holder->{$name};
}

=head3 $rslt = $eq->getAllElevations($lat, $lon, $valid);

This method was removed in version 0.116_01. Please use the
C method instead. See the L above for
details.

=head3 $rslt = $eq->getElevation($lat, $lon, $source, $elevation_only);

This method was removed in version 0.116_01. Please use the
C method instead. See the L above for
details.

=cut

=head3 $boolean = $eq->is_valid($elevation);

This method (which can also be called as a static method or as a
subroutine) returns true if the given datum represents a valid
elevation, and false otherwise. A valid elevation is a number having a
value greater than -1e+300. The input can be either an elevation value
or a hash whose {Elevation} key supplies the elevation value.

B that as of June 11 2024 I am unable to find any documentation to
support this method. Therefore use of this method is discouraged, and it
will deprecated and removed when I drop support for the C
attribute.

=cut

sub is_valid {
    my $ele = pop;
    my $ref = ref $ele;
    if ( HASH_REF eq $ref ) {
	$ele = $ele->{Elevation};
    } elsif ($ref) {
	croak "$ref reference not understood";
    }
    return defined( $ele ) && looks_like_number($ele) && $ele > -1e+300;
}

=head3 $eq = $eq->set($attribute => $value ...);

This method sets the value of the given attribute. Multiple
attribute/value pairs may be specified. The object itself is returned,
to allow call chaining. An attempt to set a non-existent attribute will
result in an exception being thrown.

=cut

{

    # Changes in these values require re-instantiating the transport
    # object. Or at least, they may do, under the following assumptions:
    # HTTP_Post: timeout.
    my %clean_transport_object = map { $_ => 1 } qw{ timeout };

    sub set {	## no critic (ProhibitAmbiguousNames)
	my ($self, @args) = @_;
	my $clean;
	while (@args) {
	    my ( $name, $val ) = splice @args, 0, 2;
	    $access_type{$name}
		or croak "No such attribute as '$name'";
	    exists $mutator{$name}
		or croak "Attribute '$name' is read-only";
	    _deprecate( attribute => $name );
	    my $holder = $access_type{$name}->( $self, $name );
	    $mutator{$name}->( $holder, $name, $val );
	    $clean ||= $clean_transport_object{$name};
	}
	$clean and delete $self->{_transport_object};
	return $self;
    }

}

sub _set_hook {
    my ( $self, $name, $val ) = @_;
    CODE_REF eq ref $val
	or croak "Attribute $name must be a code reference";
    return( $self->{$name} = $val );
}

sub _set_integer_or_undef {
    my ($self, $name, $val) = @_;
    (defined $val && $val !~ m/ \A \d+ \z /smx)
	and croak "Attribute $name must be an unsigned integer or undef";
    return ($self->{$name} = $val);
}

sub _set_literal {
    return $_[0]{$_[1]} = $_[2];
}

sub _set_throttle {
    my ( $self, $name, $val ) = @_;
    if ( defined $val ) {
	looks_like_number( $val )
	    and $val >= 0
	    or croak "The $name attribute must be undef or a ",
		'non-negative number';
	$using_time_hires
	    or $val >= 1
	    or $val == 0
	    or $val = 1;
    } else {
	$val = 0;
    }
    return( $self->{$name} = $val );
}

sub _set_unsigned_integer {
    my ($self, $name, $val) = @_;
    ( !defined $val || $val !~ m/ \A \d+ \z /smx )
	and croak "Attribute $name must be an unsigned integer";
    return ($self->{$name} = $val + 0);
}

########################################################################
#
#	Private methods
#
#	The author reserves the right to change these without notice.

{
    # NOTE to me: The deprecation of everything but 'compatible' is on
    # hold until 'compatible' gets to 2. Then everything goes to 3
    # together.
    my %dep = (
	attribute	=> {
	    dflt	=> sub { return },
	    item	=> {
		compatible	=> 0,
		default_ns	=> 3,
		proxy		=> 3,
		source		=> 3,
		use_all_limit	=> 3,
	    },
	},
	subroutine	=> {
	    dflt	=> sub {
		( my $name = ( caller( 2 ) )[3] ) =~ s/ .* :: //smx;
		return $name;
	    },
	    item	=> {
		getElevation		=> 3,
		getAllElevations	=> 3,
	    },
	},
    );

    sub _deprecate {
	my ( $group, $item ) = @_;
	my $info = $dep{$group}
	    or confess "Programming error - Deprecation group '$group' unknown";
	defined $item
	    or defined( $item = $info->{dflt}->() )
	    or croak "Programming error - No item default for group '$group'";
	$info->{item}{$item}
	    or return;
	my $msg = ucfirst "$group $item is deprecated";
	$info->{item}{$item} > 2
	    and croak "Fatal - $msg";
	warnings::enabled( 'deprecated' )
	    or return;
	carp "Warning - $msg";
	$info->{item}{$item} == 1
	    and $info->{item}{$item} = 0;
	return;
    }
}

#	$ele->_error($text);
#
#	Set the error attribute, and croak if the croak attribute is
#	true. If croak is false, just return, carping if the carp
#	attribute is true.

sub _error {
    my ($self, @args) = @_;
    $self->{error} = join '', @args;
##  $self->{croak} and croak $self->{error};
    $self->{croak} and return;
    $self->{carp} and carp $self->{error};
    return;
}

#	_instance( $object, $class )
#	    and print "\$object isa $class\n";
#
#	Return true if $object is an instance of class $class, and false
#	otherwise. Unlike UNIVERSAL::isa, this is false if the first
#	object is not a reference.

sub _instance {
    my ( $object, $class ) = @_;
    blessed( $object ) or return;
    return $object->isa( $class );
}

#	my ($self, $lat, $lon, @_) = _latlon(@_);
#
#	Strip the object reference, latitude, and longitude off the
#	argument list. If the first argument is a Geo::Point,
#	GPS::Point, or Net::GPSD::Point object the latitude and
#	longitude come from it.  Otherwise the first argument is assumed
#	to be latitude, and the second to be longitude.

{

    my %known = (
	'Geo::Point' => sub {$_[0]->latlong('wgs84')},
	'GPS::Point' => sub {$_[0]->latlon()},
	'Net::GPSD::Point' => sub {$_[0]->latlon()},
    );

    sub _latlon {
	my ($self, $obj, @args) = @_;
	foreach my $class (keys %known) {
	    if (_instance( $obj, $class ) ) {
		return ($self, $known{$class}->($obj), @args);
	    }
	}
	return ($self, $obj, @args);
    }
}

{
    my %static = (	# Static attribute values.
	throttle => 0,
    );

#	$self->_no_static_attr( $name );
#
#	Croaks if the invocant is not a reference. The message assumes
#	the method was called trying to access an attribute, whose name
#	is $name.

    sub _no_static_attr {
	my ( $self, $name ) = @_;
	ref $self
	    or croak "Attribute $name may not be accessed statically";
	return $self;
    }

#	$self->_only_static_attr( $name );
#
#	Croaks if the invocant is a reference. The message assumes the
#	method was called trying to access an attribute, whose name is
#	$name.

    sub _only_static_attr {
	my ( $self, $name ) = @_;
	ref $self
	    and croak "Attribute $name may only be accessed statically";
	return \%static;
    }

}

#	$rslt = $self->_request( %args );
#
#	This private method requests data from the USGS' web service.
#	The %args are the arguments for the request:
#	    {x} => longitude (West is negative)
#	    {y} => latitude (South is negative)
#	    {units} => desired units ('Meters' or 'Feet')
#	The return is a reference to a hash containing the parsed JSON
#	returned from the NAD server.

sub _request {
    my ( $self, %arg ) = @_;

    # The allow_nonref() is for the benefit of {_hack_result}.
    my $json = $self->{_json} ||= JSON->new()->allow_nonref();

    my $ua = $self->{_transport_object} ||=
	LWP::UserAgent->new( timeout => $self->{timeout} );

    defined $arg{units}
	or $arg{units} = 'Feet';
    $arg{units} = $arg{units} =~ m/ \A meters \z /smxi
	? 'Meters'
	: 'Feet';

    my $uri = URI->new( $self->get( 'usgs_url' ) );
    $uri->query_form( \%arg );
    my $rqst = HTTP::Request::Common::GET( $uri );

    $self->{trace}
	and print STDERR $rqst->as_string();

    my $rslt = exists $self->{_hack_result} ? do {
	my $data = delete $self->{_hack_result};
	CODE_REF eq ref $data ? $data->( $self, %arg ) : $data;
    } : $ua->request( $rqst );

    if ( $self->{trace} ) {
	if ( my $redir = $rslt->request() ) {
	    print STDERR $redir->as_string();
	}
	print STDERR $rslt->as_string();
    }

    $rslt->is_success()
	or croak $rslt->status_line();

    {
	local $@ = undef;
	eval {
	    $rslt = $json->decode( $rslt->decoded_content() );
	    ref $rslt;
	} or return $self->_error( $rslt->decoded_content() );
    }

    if ( $self->get( 'compatible' ) ) {
	$rslt = {
	    x	=>	$rslt->{location}{x},
	    y	=>	$rslt->{location}{y},
	    Data_Source	=> 'USGS Elevation Point Query Service',
	    Elevation	=> $rslt->{value},
	    Units	=> $arg{units},
	};
    } else {
	$rslt->{Elevation} = $rslt->{value};
    }

=begin comment

    foreach my $key (
	qw{ USGS_Elevation_Point_Query_Service Elevation_Query }
    ) {
	HASH_REF eq ref $rslt
	    and exists $rslt->{$key}
	    or return $self->_error(
	    "Elevation result is missing element {$key}" );
	$rslt = $rslt->{$key};
    }

    unless ( ref $rslt ) {
	$rslt =~ s/ (?
	return $self->_error( $rslt );
    }

=end comment

=cut

    my $places;
    defined $rslt->{Elevation}
	and defined( $places = $self->get( 'places' ) )
	and $rslt->{Elevation} = sprintf '%.*f', $places, $rslt->{Elevation};

    return $rslt;
}

1;

__END__