Global Navigation Satellite Systems (GNSS) refer to the collection of radio navigation systems for positioning, timing and navigation purposes. Most commonly known is the Global Positioning System for Navigation System Timing and Ranging (GPS-NAVSTAR) a.k.a. GPS. Other systems are Galileo (Europe, in development), Glonass (Russia) and Compass (China). In addition to these systems several augmentation systems exist. In Europe we have the European G... Navigation Overlay Service (EGNOS) that reduces the GPS inaccuracy to within 1 meter horizontally.