Libelium Waspmote Technical Manual page 120

The different types of NMEA statements that the Waspmote's built-in GPS receiver supports are:
NMEA GGA: provides location data and an indicator of data accuracy
•
NMEA GSA: provides the status of the satellites the GPS receiver has been connected to
•
NMEA GSV: provides information about the satellites the GPS receiver has been connected to
•
NMEA RMC: provides information about the date, time, location and speed
•
NMEA VTG: provides information about the speed and course of the GPS receiver
•
NMEA GLL: provides information about the location of the GPS receiver
•
The most important NMEA statements are the GGA statements which provide a validity indicator of the measurement
carried out, the RMC statement which provides location, speed and date/time and the GSA statement which
provides information about the status of the satellites the GPS receiver has been connected to.
(To obtain more information about the NMEA standard and the NMEA statements, visit the website:
http://www.gpsinformation.org/dale/nmea.htm)
Figure: GPS module connected to Waspmote
The GPS receiver needs time to obtain and structure the information that the satellites send. This time can be
reduced if there is certain prior information. This information is stored in the almanacs and ephemeris. The
information that can be found out is relative to the current position of the satellites (ephemeris) and the trajectory
they are going to follow over the next days (almanacs). The almanacs indicate the trajectory that the satellites are
going to follow during the next days, having a validity of some 2-3 months. The ephemeris indicate the current
position of the satellites and have a validity of some 3-5 hours.
Depending on the information that the GPS receiver has, the start ups can be divided into these types:
Hot start: once the time and date are established and the ephemeris and valid almanacs are in the me-
•
mory. Time: <1 s.
Cold start: without having established the time, date, almanacs or ephemeris. Time: <35 s.
•
As can be observed, the start up time reduces greatly, particularly when ephemeris are stored. For this reason
a series of functions have been created in the libraries to store ephemeris on the SD card and enable them to
be loaded later.
Related API libraries: WaspGPS.h, WaspGPS.cpp.
All information about their programming and operation can be found in the document: GPS Programming Guide.
All the documentation is located in the Development section in the Libelium website.
-120-
GPS
v8.2