/** GPS callback structure. */
typedef struct {
gps_location_callback location_cb;
gps_status_callback status_cb;
gps_sv_status_callback sv_status_cb;
gps_nmea_callback nmea_cb;
} GpsCallbacks;
/** Callback with location information. */
typedef void (* gps_location_callback)(GpsLocation* location);
/** Callback with status information. */
typedef void (* gps_status_callback)(GpsStatus* status);
/** Callback with SV status information. */
typedef void (* gps_sv_status_callback)(GpsSvStatus* sv_info);
/** Callback for reporting NMEA sentences. */
typedef void (* gps_nmea_callback)(GpsUtcTime timestamp, const char* nmea, int length);
3. GpsLocation 表示Locatin数据信息，底层驱动获得Location的raw信息，通常是nmea码，然后通过解析就得到了location信息。
/** Represents a location. */
typedef struct {
/** Contains GpsLocationFlags bits. */
uint16_t flags;
/** Represents latitude in degrees. */
double latitude;
/** Represents longitude in degrees. */
double longitude;
/** Represents altitude in meters above the WGS 84 reference
* ellipsoid. */
double altitude;
/** Represents speed in meters per second. */
float speed;
/** Represents heading in degrees. */
float bearing;
/** Represents expected accuracy in meters. */
float accuracy;
/** Timestamp for the location fix. */
GpsUtcTime timestamp;
} GpsLocation;