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<?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">
<!-- lifted from troff+man by doclifter -->
<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>libgps</refname>
<refpurpose>service library for communicationg with the GPS daemon</refpurpose>
</refnamediv>
<refsynopsisdiv id='synopsis'>
<funcsynopsis>
<funcsynopsisinfo>
C:
#include <gps.h>
</funcsynopsisinfo>
<funcprototype>
<funcdef>struct gps_data_t *<function>gps_open</function></funcdef>
<paramdef>char *<parameter>server</parameter></paramdef>
<paramdef>char * <parameter>port</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>int <function>gps_query</function></funcdef>
<paramdef>struct gps_data_t *<parameter>gpsdata</parameter></paramdef>
<paramdef>char *<parameter>requests</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>void <function>gps_set_raw_hook</function></funcdef>
<paramdef>struct gps_data_t *<parameter>gpsdata</parameter></paramdef>
<paramdef>void (*<parameter>hook</parameter>)(struct gps_data_t *, char *buf)</paramdef>
</funcprototype>
<funcprototype>
<funcdef>int <function>gps_poll</function></funcdef>
<paramdef>struct gps_data_t *<parameter>gpsdata</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>void <function>gps_close</function></funcdef>
<paramdef>struct gps_data_t *<parameter>gpsdata</parameter></paramdef>
</funcprototype>
<funcsynopsisinfo>
Python:
import gps
session = gps.gps(host="localhost", port="2947")
session.set_raw_hook(raw_hook)
session.query(commands)
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 high-level
interface that is safe for multiple applications to use simultaneously; it
is probably the one you want. The low-level interface is documented
at
<citerefentry><refentrytitle>libgps</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
<para>Calling <function>gpsd_open()</function> initializes a GPS-data
structure to hold the data collected by the GPS, and returns a socket
attached to
<citerefentry><refentrytitle>gpsd</refentrytitle><manvolnum>1</manvolnum></citerefentry>.
<function>gpsd_open()</function> returns NULL on errors. errno is
set depending on the error returned from the the socket layer; see
<filename>gps.h</filename> for values and explanations.</para>
<para><function>gpsd_close()</function> ends the session.</para>
<para><function>gpsd_poll()</function> accepts a response, or sequence
of responses, from the daemon and interprets it as though it were a
query response (the return value is as for a query).
<function>gpsd_poll()</function> returns the validity mask of the
received structure. This function does a blocking read waiting for
data from the daemon; it returns 0 for success, or -1 on a Unix-level
read error. </para>
<para><function>gpsd_query()</function> writes a command to the
daemon, accepts a one-line response, and updates parts of the GPS-data
structure that correspond to data changed since the last call. The
second argument must be a string containing letters from the command
set documented at
<citerefentry><refentrytitle>gpsd</refentrytitle><manvolnum>1</manvolnum></citerefentry>.
This function returns a 0 on success, or a -1 if there was a
Unix-level read error.</para>
<para>Consult <filename>gps.h</filename> to learn more about the data members
and associated timestamps. Note that information will accumulate
in the session structure over time, and the 'valid' field is not
automatically zeroed by each poll. It is up to the client to
zero that field when appropriate and to keep an eye on the fix
and sentence timestamps.</para>
<para>The Python implementation supports the same facilities as the C
library. <function>gps_open()</function> is replaced by the
initialization of a gps 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>libgps</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
</para>
</refsect1>
<refsect1 id='author'><title>AUTHOR</title>
<para>Eric S. Raymond <esr@thyrsus.com>.</para>
</refsect1>
</refentry>
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