Steve Bertrand

NAME

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

Coverage Status

SYNOPSIS

    use GPSD::Parse;

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

    # start the data flow, and poll for data

    $gps->on;
    $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;

    # stop capturing data

    $gps->off;

DESCRIPTION

Simple, lightweight distribution that polls gpsd for data received from a UART (serial) 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 -n /dev/ttyS0 -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.

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.

on

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

If this method is not called, a warning will be thrown when you poll(), and your dataset will be incomplete (ie. invalid).

off

Turns off gpsd listening mode.

Not necessary to call, but it will help preserve battery life if running on a portable device.

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.

    fname => $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.

    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 undef 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

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.

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.