14 Aug 2004 3 3 Linux libgps service library for communicationg with the GPS daemon C: #include <gps.h> struct gps_data_t *gps_open char *server char * port int gps_query struct gps_data_t *gpsdata char *requests void gps_set_raw_hook struct gps_data_t *gpsdata void (*hook)(struct gps_data_t *, char *buf) int gps_poll struct gps_data_t *gpsdata void gps_close struct gps_data_t *gpsdata Python: import gps session = gps.gps(host="localhost", port="2947") session.set_raw_hook(raw_hook) session.query(commands) session.poll() del session libgps 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 gpsd1 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 libgps3. Calling gpsd_open() initializes a GPS-data structure to hold the data collected by the GPS, and returns a socket attached to gpsd1. gpsd_open() returns NULL on errors. errno is set depending on the error returned from the the socket layer; see gps.h for values and explanations. gpsd_close() ends the session. gpsd_poll() 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). gpsd_poll() 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. gpsd_query() 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 gpsd1. This function returns a 0 on success, or a -1 if there was a Unix-level read error. Consult gps.h 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. The Python implementation supports the same facilities as the C library. gps_open() 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. gpsd8, xgps1, libgps3. Eric S. Raymond <esr@thyrsus.com>.