Methods

$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.

%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.

$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. This hash will contain the following keys:

{Data_Source} => A text description of the data source;

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

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

{x} => The $lon argument;

{y} => The $lat argument.

You can also pass a "Geo::Point", "GPS::Point", or "Net::GPSD::Point" object in lieu of the $lat and $lon arguments. If you do this, $valid becomes the second argument, rather than the third.

If the optional $valid argument is specified and the returned data are invalid, nothing is returned. The NAD source does not seem to produce data recognizable as invalid, so you will probably not see this.

The NAD server appears to return an elevation of 0 if the elevation is unavailable.

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

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

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

This method was removed in version 0.116_01. Please use the "elevation()" method instead. See the NOTICE above for details.

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

This method was removed in version 0.116_01. Please use the "elevation()" method instead. See the NOTICE above for details.

$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.

$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.

Attributes

Boolean

This Boolean attribute determines whether the data acquisition methods carp on encountering an error. If false, they silently return undef. Note, though, that the croak attribute trumps this one.

If retry is set to a number greater than 0, you will get a carp on each failed query, provided croak is false. If croak is true, no retries will be carped.

This attribute was introduced in Geo::WebService::Elevation::USGS version 0.005_01.

The default is 0 (i.e. false).

compatible

This attribute was removed in version 0.116_01. It existed to support interaction with the now-long-defunct GIS web service. See the NOTICE above for details.

croak

Boolean

This Boolean attribute determines whether the data acquisition methods croak on encountering an error. If false, they return undef on an error.

If retry is set to a number greater than 0, the data acquisition method will not croak until all retries are exhausted.

The default is 1 (i.e. true).

default_ns

This attribute was removed in version 0.116_01. It existed to support interaction with the now-long-defunct GIS web service. See the NOTICE above for details.

error

String

This attribute records the error returned by the last query operation, or undef if no error occurred. This attribute can be set by the user, but will be reset by any query operation.

The default (before any queries have occurred) is undef.

places

Integer

If this attribute is set to a non-negative integer, elevation results will be rounded to this number of decimal places by running them through sprintf "%.${places}f".

The default is undef.

proxy

This attribute was removed in version 0.116_01. It existed to support interaction with the now-long-defunct GIS web service. See the NOTICE above for details.

retry

Unsigned integer

This attribute specifies the number of retries to be done by "elevation()" when an error is encountered. The first try is not considered a retry, so if you set this to 1 you get a maximum of two queries (the try and the retry).

Retries are done only on actual errors, not on bad extents. They are also subject to the "throttle" setting if any.

The default is 0, i.e. no retries.

retry_hook

Code reference

This attribute specifies a piece of code to be called before retrying. The code will be called before a retry takes place, and will be passed the Geo::WebService::Elevation::USGS object, the number of the retry (from 1), the name of the method being retried ('elevation' and the arguments to that method. If the position was passed as an object, the hook gets the latitude and longitude unpacked from the object. The hook will not be called before the first try, nor after the last retry.

Examples:

 # To sleep 5 seconds between retries:
 $eq->set( retry_hook => sub { sleep 5 } );
 
 # To sleep 1 second before the first retry, 2 seconds
 # before the second, and so on:
 $eq->set( retry_hook => sub { sleep $_[1] } );
 
 # To do nothing between retries:
 $eq->set( retry_hook => sub {} );

The default is the null subroutine, i.e. "sub {}".

source

This attribute was removed in version 0.116_01. It existed to support interaction with the now-long-defunct GIS web service. See the NOTICE above for details.

throttle

Non-negative number, or undef

 Geo::WebService::Elevation::USGS->set( throttle => 5 );

This attribute, if defined and positive, specifies the minimum interval between queries, in seconds. This attribute may be set statically only, and the limit applies to all queries, not just the ones from a given object. If Time::HiRes can be loaded, then sub-second intervals are supported, otherwise not.

This functionality, and its implementation, are experimental, and may be changed or retracted without notice. Heck, I may even go back to $TARGET, though I don't think so.

timeout

Integer, or undef

This attribute specifies the timeout for the query in seconds.

The default is 30.

trace

Boolean

If true, this Boolean attribute requests that network requests and responses be dumped to standard error. This should only be used for troubleshooting, and the author makes no representation about and has no control over what output you get if you set this true.

The default is "undef" (i.e. false).

units

String

This attribute specifies the desired units for the resultant elevations. Valid values are 'Feet' and 'Meters'. In practice these are not case-sensitive, and any value other than case-insensitive 'Meters' will be taken as 'Feet'.

The default is 'FEET', but this will become 'Feet' when the compatibility code goes away.

use_all_limit

This attribute was removed in version 0.116_01. It existed to support interaction with the now-long-defunct GIS web service. See the NOTICE above for details.

usgs_url

This attribute specifies the URL to query. Under normal circumstances you will not need to change this, but maybe it can get you going again if the USGS moves the service.

The default is the value of environment variable "GEO_WEBSERVICE_ELEVATION_USGS_URL". If that is undefined, the default is "https://nationalmap.gov/epqs/pqs.php". Note that without query parameters this URL does nothing useful. See <https://nationalmap.gov/epqs/> for details.