path: root/libgpsd.xml

<?xml version="1.0" encoding="ISO-8859-1"?>
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN"
                   "http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd">
<refentry>
<refentryinfo><date>14 Aug 2004</date></refentryinfo>
<refmeta>
<refentrytitle>3</refentrytitle>
<manvolnum>3</manvolnum>
<refmiscinfo class='source'>Linux</refmiscinfo>
</refmeta>
<refnamediv id='name'>
<refname>libgpsd</refname>
<refpurpose>service library for GPS applications</refpurpose>
</refnamediv>
<refsynopsisdiv id='synopsis'>
<funcsynopsis>
<funcsynopsisinfo>
C:

#include &lt;gpsd.h&gt;

</funcsynopsisinfo>
<funcprototype>
<funcdef>struct gps_session_t * <function>gpsd_init</function></funcdef>
    <paramdef>char * <parameter>dgpsserver</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>int <function>gpsd_activate</function></funcdef>
    <paramdef>struct gps_session_t * <parameter>session</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>void <function>gpsd_deactivate</function></funcdef>
    <paramdef>struct gps_session_t * <parameter>session</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>int <function>gpsd_poll</function></funcdef>
    <paramdef>struct gps_session_t * <parameter>session</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>void <function>gpsd_wrap</function></funcdef>
    <paramdef>struct gps_session_t * <parameter>session</parameter></paramdef>
</funcprototype>

<funcprototype>
<funcdef>void <function>gpsd_report</function></funcdef>
    <paramdef>int <parameter>d</parameter></paramdef>
    <paramdef>const char * <parameter>fmt</parameter></paramdef>
    <paramdef><parameter>...</parameter></paramdef>
</funcprototype>

<funcsynopsisinfo>
Python:

import gpsd

session = gpsd.gpsd(device="/dev/gps", dgps=None, logger=None)
session.activate()

session.deactivate()

session.poll()

del session
</funcsynopsisinfo>
</funcsynopsis>
</refsynopsisdiv>

<refsect1 id='description'><title>DESCRIPTION</title>
<para><emphasis remap='B'>libgps</emphasis>
is a service library which supports querying GPS devices; link it with
the linker option -lgps. There are
two interfaces supported in it; one high-level interface that
goes through
<citerefentry><refentrytitle>gpsd</refentrytitle><manvolnum>1</manvolnum></citerefentry>
and is intended for concurrent use by several applications, and one
low-level interface that speaks directly with the serial or USB device
to which the GPS is attached.  This page describes the low-level
interface, which
<citerefentry><refentrytitle>gpsd</refentrytitle><manvolnum>1</manvolnum></citerefentry>
itself uses.  See 
<citerefentry><refentrytitle>gpsd</refentrytitle><manvolnum>3</manvolnum></citerefentry>
for a description of the high-level interface, which is almost
certainly what you want.</para>

<para>Calling
<function>gpsd_init()</function>
initializes a session structure to hold the data collected by the GPS.</para>

<para>You must specify a device type by key letter; to list key
letters, run <command>gpsd -h</command>.  It is generally safe to
specify 'n', as most modern GPSes speak NMEA.  (The Python binding
no longer requires setting a device type; this is a future direction
for the C binding)</para>

<para>You may optionally specify a DGPS server, either as a string
containing a server name or a string containining server name followed
by a colon and a port name or number.  To specify no DGPS, pass the 
null pointer.</para>

<para>After the session structure has been set up, you may modify some
of its members.</para>

<variablelist>
<varlistentry>
<term><structfield>gpsd_device</structfield></term>
<listitem>
<para>This member should hold the path name of the device; it defaults to
<filename>/dev/gps</filename>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><structfield>baudrate</structfield></term>
<listitem>
<para>Communication speed in bits per second.  For NMEA or SiRF devices, the
library automatically hunts through all plausible baud rates, stopping
on the one where it sees valid packets.  By setting this field you can
designate a speed to be tried at the front of the hunt queue</para>
</listitem>
</varlistentry>
<varlistentry>
<term><structfield>raw_hook</structfield></term>
<listitem>
<para>A hook function to be executed on each NMEA
sentence as it is read from the GPS.  The data from non-NMEA GPSes like
the EarthMate will be translated to an NMEA sentence before being
passed to the hook.</para>
</listitem>
</varlistentry>
</variablelist>

<para><function>gpsd_activate()</function>
initializes the connection to the GPS.  
<function>gpsd_deactivate()</function>
closes the connection. These functions are provided so that
long-running programs can release a connection when there is no
activity requiring the GPS, and re-acquire it later.</para>

<para><function>gpsd_poll()</function>
queries the GPS and updates the part of the session structure that
holds position, speed, GPS signal quality, and other data returned
by the GPS. It returns a mask describing which fields have changed.</para>

<para><function>gpsd_wrap()</function>
ends the session, implicitly performing a 
<function>gpsd_deactivate()</function>.</para>

<para>The calling application must define one additional function:
<function>gpsd_report()</function>.
The library will use this to issue ordinary status messages.  Use 
first argument of 0 for errors, 1 for ordinary status messages,
and 2 or higher for debugging messages.</para>

<para>The Python implementation supports the same facilities as the C
library, but only for straight NMEA devices with a 1-second send cycle
(no Zodiac or Garmin binary-protocol support).
<function>gps_init()</function> is replaced by the initialization of a
gpsd session object; the other calls are methods of that object.
Resources within the session object will be properly released when it
is garbage-collected.</para>
</refsect1>

<refsect1 id='see_also'><title>SEE ALSO</title>
<para>
<citerefentry><refentrytitle>gpsd</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
<citerefentry><refentrytitle>xgps</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
<citerefentry><refentrytitle>libgpsd</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
</para>
</refsect1>

<refsect1 id='author'><title>AUTHOR</title>
<para>Eric S. Raymond &lt;esr@thyrsus.com&gt; based partly on earlier work by
Remco Treffkorn, Derrick Brashear, and Russ Nelson.</para>
</refsect1>
</refentry>