Editing Global Positioning System (section)

=== User segment ===
{{further|GPS navigation device}}

[[File:GPS Receivers.jpg|thumb|right|upright=0.8|GPS receivers come in a variety of formats, from devices integrated into cars, phones, and watches, to dedicated devices such as those shown above.]]
[[File:Leica WM 101 at the National Science Museum at Maynooth.JPG|thumb|right|The first portable GPS survey unit, a Leica WM 101, displayed at the [[Irish National Science Museum]] at [[Maynooth]]]]

The user segment (US) is composed of hundreds of thousands of U.S. and allied military users of the secure GPS Precise Positioning Service, and tens of millions of civil, commercial and scientific users of the Standard Positioning Service. In general, GPS receivers are composed of an antenna, tuned to the frequencies transmitted by the satellites, receiver-processors, and a highly stable clock (often a [[crystal oscillator]]). They may also include a display for providing location and speed information to the user.

GPS receivers may include an input for differential corrections, using the [[RTCM]] SC-104 format. This is typically in the form of an [[RS-232]] port at 4,800&nbsp;bit/s speed. Data is actually sent at a much lower rate, which limits the accuracy of the signal sent using RTCM.{{Citation needed|date=August 2011}} Receivers with internal DGPS receivers can outperform those using external RTCM data.{{Citation needed|date=August 2011}} {{As of |2006}}, even low-cost units commonly include [[Wide Area Augmentation System]] (WAAS) receivers.

[[File:SiRF Star III основанный на GPS приёмнике с интегрированной антенной.jpg|thumb|right|upright=0.8|A typical GPS receiver with integrated antenna]]

Many GPS receivers can relay position data to a PC or other device using the [[NMEA 0183]] protocol. Although this protocol is officially defined by the National Marine Electronics Association (NMEA),<ref>{{cite web|url=http://www.nmea.org/content/nmea_standards/nmea_standards.asp|title=Publications and Standards from the National Marine Electronics Association (NMEA)|publisher=National Marine Electronics Association|access-date=June 27, 2008|archive-url=https://web.archive.org/web/20090804071335/http://www.nmea.org/content/nmea_standards/nmea_standards.asp|archive-date=August 4, 2009}}</ref> references to this protocol have been compiled from public records, allowing open source tools like [[gpsd]] to read the protocol without violating intellectual property laws.{{Clarify|What does it mean to "compile references to a protocol"?|date=February 2013}} Other proprietary protocols exist as well, such as the [[SiRF]] and [[MediaTek|MTK]] protocols. Receivers can interface with other devices using methods including a serial connection, [[Universal Serial Bus|USB]], or [[Bluetooth]].