The Global Positioning System: www.aero.org/publications/GPSPRIMER/index.html, www.navcen.uscg.gov/gps/default.htm, www.navcen.uscg.gov/gps/geninfo, https://gps.losangeles.af.mil/jpo and news://sci.geo.satellite-nav
GPS Data Sources: cddisa.gsfc.nasa.gov, www.ga.gov.au/nmd/geodesy/argn, igscb.jpl.nasa.gov and earth-info.nga.mil/GandG/sathtml
GPS Data Formats: www.aiub.unibe.ch/download/rinex, www.nmea.org/pub/0183/index.html and home.mira.net/~gnb/gps/nmea.html
GPS Receivers and Open Source: sharc.sourceforge.net, www.sirf.com, gpsbabel.sourceforge.net, gpsdrive.kraftvoll.at, www.cstr.ed.ac.uk/projects/festival, wigle.net, home.earthlink.net/~cwkelley, www.mgix.com/gps3d, www.pygps.org/gpsd/protocol.html and www.unavco.org/facility/software/teqc/teqc.html
Getting Started with GPSTk: gpstk.sourceforge.net, www.perforce.com/jam/jam.html and www.doxygen.org
Future of GPS and GNSS: europa.eu.int/comm/dgs/energy_transport/galileo/index_en.htm