NAME
    GPSD::Parse - Parse, extract use the JSON output from GPS units

SYNOPSIS
        use GPSD::Parse;
        my $gps = GPSD::Parse->new;

        # poll for data

        $gps->poll;

        # get all TPV data in an href

        my $tpv_href = $gps->tpv;

        # get individual TPV stats

        print $gps->tpv('lat');
        print $gps->tpv('lon');

        # timestamp of the most recent poll

        print $gps->time;

        # get all satellites in an href of hrefs

        my $sats = $gps->satellites;

        # get an individual piece of info from a single sattelite

        print $gps->satellites(16, 'ss');

        # check which serial device the GPS is connected to

        print $gps->device;

DESCRIPTION
    Simple, lightweight (core only) distribution that polls `gpsd' for data
    received from a UART (serial/USB) connected GPS receiver over a TCP
    connection.

    The data is fetched in JSON, and returned as Perl data.

NOTES
  Requirements
    A version of gpsd that returns results in JSON format is required to
    have been previously installed. It should be started at system startup,
    with the following flags with system-specific serial port. See the above
    link for information on changing the listen IP and port.

        sudo gpsd /dev/ttyS0 -n -F /var/log/gpsd.sock

  Available Data
    Each of the methods that return data have a table in their respective
    documentation within the METHODS section. Specifically, look at the
    `tpv()', `sattelites()' and the more broad `sky()' method sections to
    understand what available data attributes you can extract.

  Conversions
    All output where applicable defaults to metric (metres). See the
    `metric' parameter in the `new()' method to change this to use
    imperial/standard measurements.

    For latitude and longitude, we default to using the signed notation. You
    can disable this with the `signed' parameter in `new()'.

METHODS
  new(%args)
    Instantiates and returns a new GPSD::Parse object instance.

    Parameters:

        host => 127.0.0.1

    Optional, String: An IP address or fully qualified domain name of the
    `gpsd' server. Defaults to the localhost (`127.0.0.1') if not supplied.

        port => 2947

    Optional, Integer: The TCP port number that the `gpsd' daemon is running
    on. Defaults to `2947' if not sent in.

        metric => Bool

    Optional, Integer: By default, we return measurements in metric
    (metres). Send in a false value (`0') to use imperial/standard
    measurement conversions (ie. feet). Note that if returning the raw
    *JSON* data from the `poll()' method, the conversions will not be done.
    The default raw Perl return will have been converted however.

        signed => Bool

    Optional, Integer: By default, we use the signed notation for latitude
    and longitude. Send in a false value (`0') to disable this. Here's an
    example:

        enabled (default)   disabled
        -----------------   --------

        lat: 51.12345678    51.12345678N
        lon: -114.123456    114.123456W

    We add the letter notation at the end of the result if `signed' is
    disabled.

        file => 'filename.ext'

    Optional, String: For testing purposes. Instead of reading from a
    socket, send in a filename that contains legitimate JSON data saved from
    a previous `gpsd' output and we'll operate on that. Useful also for
    re-running previous output.

  poll(%args)
    Does a poll of `gpsd' for data, and configures the object with that
    data.

    Parameters:

    All parameters are sent in as a hash.

        file => $filename

    Optional, String: Used for testing, you can send in the name of a JSON
    file that contains `gpsd' JSON data and we'll work with that instead of
    polling the GPS device directly. Note that you *must* instantiate the
    object with the `file' parameter in new for this to have any effect and
    to bypass the socket creation.

        return => 'json'

    Optional, String: By default, after configuring the object, we will
    return the polled raw data as a Perl hash reference. Send this param in
    with the value of `'json'' and we'll return the data exactly as we
    received it from `gpsd'.

    Returns:

    The raw poll data as either a Perl hash reference structure or as the
    original JSON string.

  tpv($stat)
    `TPV' stands for "Time Position Velocity". This is the data that
    represents your location and other vital statistics.

    By default, we return a hash reference that is in the format `stat ='
    'value'>.

    Parameters:

        $stat

    Optional, String. You can extract individual statistics of the TPV data
    by sending in the name of the stat you wish to fetch. This will then
    return the string value if available. Returns an empty string if the
    statistic doesn't exist.

    Available statistic/info name, example value, description. This is the
    default raw result:

       time     => '2017-05-16T22:29:29.000Z'   # date/time in UTC
       lon      => '-114.000000000'             # longitude
       lat      => '51.000000'                  # latitude
       alt      => '1084.9'                     # altitude (metres)
       climb    => '0'                          # rate of ascent/decent (metres/sec)
       speed    => '0'                          # rate of movement (metres/sec)
       track    => '279.85'                     # heading (degrees from true north)
       device   => '/dev/ttyS0'                 # GPS serial interface            
       mode     => 3                            # NMEA mode
       epx      => '3.636'                      # longitude error estimate (metres)
       epy      => '4.676'                      # latitude error estimate (metres)
       epc      => '8.16'                       # ascent/decent error estimate (meters)
       ept      => '0.005'                      # timestamp error (sec) 
       epv      => '4.082'                      # altitude error estimate (meters)
       eps      => '9.35'                       # speed error estimate (metres/sec)
       class    => 'TPV'                        # data type (fixed as TPV)
       tag      => 'ZDA'                        # identifier

  satellites($num, $stat)
    This method returns a hash reference of hash references, where the key
    is the satellite number, and the value is a hashref that contains the
    various information related to the specific numbered satellite.

    Note that the data returned by this function has been manipuated and is
    not exactly equivalent of that returned by `gpsd'. To get the raw data,
    see `sky()'.

    Parameters:

        $num

    Optional, Integer: Send in the satellite number and we'll return the
    relevant information in a hash reference for the specific satellite
    requested, as opposed to returning data for all the satellites. Returns
    `undef' if a satellite by that number doesn't exist.

        $stat

    Optional, String: Like `tpv()', you can request an individual piece of
    information for a satellite. This parameter is only valid if you've sent
    in the `$num' param, and the specified satellite exists.

    Available statistic/information items available for each satellite,
    including the name, an example value and a description:

    NOTE: The PRN attribute will not appear unless you're using raw data.
    The PRN can be found as the satellite hash reference key after we've
    processed the data.

        PRN     => 16   # PRN ID of the satellite 

                        # 1-63 are GNSS satellites
                        # 64-96 are GLONASS satellites
                        # 100-164 are SBAS satellites

        ss      => 20   # signal strength (dB)
        az      => 161  # azimuth (degrees from true north)
        used    => 1    # currently being used in calculations
        el      => 88   # elevation in degrees

  sky
    Returns a hash reference containing all of the data that was pulled from
    the `SKY' information returned by `gpsd'. This information contains
    satellite info and other related statistics.

    Available information, with the attribute, example value and
    description:

        satellites  => []           # array of satellite hashrefs
        xdop        => '0.97'       # longitudinal dilution of precision
        ydop        => '1.25'       # latitudinal dilution of precision
        pdop        => '1.16'       # spherical dilution of precision
        tdop        => '2.2'        # time dilution of precision
        vdop        => '0.71'       # altitude dilution of precision
        gdop        => '3.87'       # hyperspherical dilution of precision
        hdop        => '0.92'       # horizontal dilution of precision
        class       => 'SKY'        # object class, hardcoded to SKY
        tag         => 'ZDA'        # object ID
        device      => '/dev/ttyS0' # serial port connected to the GPS

  direction($degree)
    Converts a degree from true north into a direction (eg: ESE, SW etc).

    Parameters:

        $degree

    Mandatory, Ineger/Decimal: A decimal ranging from 0-360. Returns the
    direction representing the degree from true north. A common example
    would be:

        my $heading = $gps->direction($gps->tpv('track'));

    Degree/direction map:

        N       348.75 - 11.25
        NNE     11.25  - 33.75
        NE      33.75  - 56.25
        ENE     56.25  - 78.75

        E       78.75  - 101.25
        ESE     101.25 - 123.75
        SE      123.75 - 146.25
        SSE     146.25 - 168.75

        S       168.75 - 191.25
        SSW     191.25 - 213.75
        SW      213.75 - 236.25
        WSW     236.25 - 258.75

        W       258.75 - 281.25
        WNW     281.25 - 303.75
        NW      303.75 - 326.25
        NNW     326.25 - 348.75

  device
    Returns a string containing the actual device the GPS is connected to
    (eg: `/dev/ttyS0').

  time
    Returns a string of the date and time of the most recent poll, in UTC.

  on
    Puts `gpsd' in listening mode, ready to poll data from.

    We call this method internally when the object is instantiated with
    `new()' if we're not in file mode. Likewise, when the object is
    destroyed (end of program run), we call the subsequent `off()' method.

    If you have long periods of a program run where you don't need the GPS,
    you can manually run the `off()' and `on()' methods to disable and
    re-enable the GPS.

  off
    Turns off `gpsd' listening mode.

    Not necessary to call, but it will help preserve battery life if running
    on a portable device for long program runs where the GPS is used
    infrequently. Use in conjunction with `on()'. We call `off()'
    automatically when the object goes out of scope (program end for
    example).

EXAMPLES
  Basic Features and Options
    Here's a simple example using some of the basic features and options.
    Please read through the documentation of the methods (particularly
    `new()' and `tpv()' to get a good grasp on what can be fetched.

        use warnings;
        use strict;
        use feature 'say';

        use GPSD::Parse;

        my $gps = GPSD::Parse->new(signed => 0);

        $gps->poll;

        my $lat = $gps->tpv('lat');
        my $lon = $gps->tpv('lon');

        my $heading = $gps->tpv('track');
        my $direction = $gps->direction($heading);

        my $altitude = $gps->tpv('alt');

        my $speed = $gps->tpv('speed');

        say "latitude:  $lat";
        say "longitude: $lon\n";

        say "heading:   $heading degrees";
        say "direction: $direction\n";

        say "altitude:  $altitude metres\n";

        say "speed:     $speed metres/sec";

    Output:

        latitude:  51.1111111N
        longitude: 114.11111111W

        heading:   31.23 degrees
        direction: NNE

        altitude:  1080.9 metres

        speed:     0.333 metres/sec

TESTING
    Please note that we init and disable the GPS device on construction and
    deconstruction of the object respectively. It takes a few seconds for
    the GPS unit to initialize itself and then lock on the satellites before
    we can get readings. For this reason, please understand that one test
    sweep may pass while the next fails.

    I am considering adding specific checks, but considering that it's a
    timing thing (seconds, not microseconds that everyone is in a hurry for
    nowadays) I am going to wait until I get a chance to take the kit into
    the field before I do anything drastic.

    For now. I'll leave it as is; expect failure if you ram on things too
    quickly.

SEE ALSO
    A very similar distribution is Net::GPSD3. However, it has a long line
    of prerequisite distributions that didn't always install easily on my
    primary target platform, the Raspberry Pi.

    This distribution isn't meant to replace that one, it's just a much
    simpler and more lightweight piece of software that pretty much does the
    same thing.

AUTHOR
    Steve Bertrand, `<steveb at cpan.org>'

LICENSE AND COPYRIGHT
    Copyright 2017 Steve Bertrand.

    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.

