GPSD::Parse - Parse, extract use the JSON output from GPS units
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'); # ...or print $gps->lat; print $gps->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; # toggle between metres and feet (metres by default) $gps->feet; $gps->metres;
Simple, lightweight (core only) distribution that polls gpsd for data received from a UART (serial/USB) connected GPS receiver over a TCP connection.
gpsd
The data is fetched in JSON, and returned as Perl data.
A version of gpsd that returns results in JSON format is required to have been previously installed. It should be started at system startup, with the following flags with system-specific serial port. See the above link for information on changing the listen IP and port.
sudo gpsd /dev/ttyS0 -n -F /var/log/gpsd.sock
NOTE: The -n flag *must* be present when running gpsd. If not, this software will stay in an endless loop of "Waiting for a valid GPS signal", even if the GPS device has been triangulated. See your Operating Systems startup system to add this flag to the startup if necessary (on Ubuntu, add "-n" to the GPSD_OPTIONS section in /etc/defaults/gpsd).
-n
GPSD_OPTIONS
/etc/defaults/gpsd
Each of the methods that return data have a table in their respective documentation within the "METHODS" section. Specifically, look at the "tpv($stat)", "satellites($num, $stat)" and the more broad "sky" method sections to understand what available data attributes you can extract.
All output where applicable defaults to metric (metres). See the metric parameter in the "new(%args)" method to change this to use imperial/standard measurements. You can also toggle this at runtime with the "feet" and "metres" methods.
metric
For latitude and longitude, we default to using the signed notation. You can disable this with the signed parameter in "new(%args)", along with the "signed" and "unsigned" methods to toggle this conversion at runtime.
signed
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.
127.0.0.1
port => 2947
Optional, Integer: The TCP port number that the gpsd daemon is running on. Defaults to 2947 if not sent in.
2947
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(%args)" method, the conversions will not be done. The default raw Perl return will have been converted however.
0
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.
NOTE: You can toggle this at runtime by calling the "signed" and "unsigned" methods. The data returned at the next poll will reflect any change.
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.
Does a poll of gpsd for data, and configures the object with that data.
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.
file
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.
'json'
Returns:
The raw poll data as either a Perl hash reference structure or as the original JSON string.
Returns the longitude. Alias for $gps->tpv('lon').
$gps->tpv('lon')
Returns the latitude. Alias for $gps->tpv('lat').
$gps->tpv('lat')
Returns the altitude. Alias for $gps->tpv('alt').
$gps->tpv('alt')
Returns the rate of ascent/decent. Alias for $gps->tpv('climb').
$gps->tpv('climb')
Returns the rate of movement. Alias for $gps->tpv('speed').
$gps->tpv('speed')
Returns the direction of movement, in degrees. Alias for $gps->tpv('track').
$gps->tpv('track')
TPV stands for "Time Position Velocity". This is the data that represents your location and other vital statistics.
TPV
By default, we return a hash reference. The format of the hash is depicted below. Note also that the most frequently used stats also have their own methods that can be called on the object as opposed to having to reach into a hash reference.
$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
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".
$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.
undef
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.
tpv()
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
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.
SKY
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
Converts a degree from true north into a direction (eg: ESE, SW etc).
$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->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
Returns a string containing the actual device the GPS is connected to (eg: /dev/ttyS0).
/dev/ttyS0
Returns a string of the date and time of the most recent poll, in UTC.
This method works on the latitude and longitude output view. By default, we use signed notation, eg:
-114.1111111111 # lon 51.111111111111 # lat
If you've switched to "unsigned", calling this method will toggle it back, and the results will be visible after the next "poll(%args)"
You can optionally use this method to convert values in a manual way. Simply send in the latitude and longitude in that order as parameters, and we'll return a list containing them both after modification, if it was necessary.
Calling this method will convert those to:
114.1111111111W # lon 51.11111111111N # lat
If you've switched to "signed" calling this method will toggle it back, and the results will be visible after the next "poll(%args)".
By default, we use metres as the measurement for any attribute that is measured in distance. Call this method to have all attributes converted into feet commencing at the next call to "poll(%args)". Use "metres" to revert back.
We measure in metres by default. If you've switched to using feet as the measurement unit, a call to this method will revert back to the default.
Puts gpsd in listening mode, ready to poll data from.
We call this method internally when the object is instantiated with "new(%args)" 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.
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).
Here's a simple example using some of the basic features and options. Please read through the documentation of the methods (particularly "new(%args)" and "tpv($stat)" 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->lat; my $lon = $gps->lon; my $heading = $gps->track; # degrees my $direction = $gps->direction($heading); # ENE etc my $altitude = $gps->alt; my $speed = $gps->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
Here's a rough example that displays the status of tracked satellites, along with the information on the ones we're currently using.
use warnings; use strict; use GPSD::Parse; my $gps = GPSD::Parse->new; while (1){ $gps->poll; my $sats = $gps->satellites; for my $sat (keys %$sats){ if (! $gps->satellites($sat, 'used')){ print "$sat: unused\n"; } else { print "$sat: used\n"; for (keys %{ $sats->{$sat} }){ print "\t$_: $sats->{$sat}{$_}\n"; } } } sleep 3; }
7: used ss: 20 used: 1 az: 244 el: 20 29: unused 31: used el: 12 az: 64 used: 1 ss: 17 6: unused 138: unused 16: used ss: 17 el: 53 used: 1 az: 119 26: used az: 71 used: 1 el: 46 ss: 27 22: used ss: 28 el: 17 used: 1 az: 175 3: used ss: 24 az: 192 used: 1 el: 40 9: unused 23: unused 2: unused
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.
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.
Steve Bertrand, <steveb at cpan.org>
<steveb at cpan.org>
Copyright 2019 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.
To install GPSD::Parse, copy and paste the appropriate command in to your terminal.
cpanm
cpanm GPSD::Parse
CPAN shell
perl -MCPAN -e shell install GPSD::Parse
For more information on module installation, please visit the detailed CPAN module installation guide.