Functions:-This file provides the interface to Differential GNSS (Global Navigation Satellite Systems) services. Notes based on $Id: dgnss.c 3771 2006-11-02 05:15:20Z esr $ bool dgnss_url(char *name) Check if a URL is valid for DGPS service. int dgnss_open(struct gps_context_t *context, char *dgnss_service) Try to open a connection to the nominated service. If the service cannot be opened, the return is -1. The supported services are dgpsip (differential corrections via IP) and ntrip (differential corrections in http form). int dgnss_poll(struct gps_context_t *context) Try to poll the DGNSS service for a correction report. If no socket is active, simply return 0. If a socket is active, on successful read it stores the current timestamp and the report in the context buffer then returns 0. If no data is ready or an error (except EAGAIN) occurs, drop the connection and return -1. void dgnss_report(struct gps_device_t *session) Call the dgpsip_report() or ntrip_report() function if either is active. void dgnss_autoconnect(struct gps_context_t *context, double lat, double lon) Call the autoconnect() function in dgpsip.c void rtcm_relay(struct gps_device_t *session) If there is a DGNSS connection report in the context buffer, pass it to the caller. If the transaction fails, generate an error log, otherwise, update the session timestamp.