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Radionavigation The determination of position, or the obtaining of information relative to position, for the purpose of navigation by means of the propagation properties of radio waves. GPS is a method of radionavigation.
RAIM Receiver Autonomous Integrity Monitoring
Range A fixed distance between two points, such as between a starting and an ending waypoint or a satellite and a GPS reciever.
Range Rate The rate of change of range (distance) between the satellite and receiver. The distance to a satellite changes because the satellites are moving across the sky and the earth is rotating. Range rate is determined by measuring the Doppler shift of the satellite signal.
RDOP Relative dilution of precision. See DOP
Real-time differential GPS This is also known as "RTK" mapping. A base station which computes, formats, and transmits corrections usually through some sort of data link (e.g. VHF radio or cellular telephone) with each new GPS observation. The roving unit requires some sort of data link receiving equipment to receive the transmitted GPS corrections and get them into the GPS receiver so they can be applied to its current observations.
Reconstructed carrier phase The difference between the phase of the incoming GPS carrier, corrected for Doppler shift, and the phase of a nominally constant reference frequency generated in the receiver.

For static positioning, The reconstructed carrier phase is sampled at epochs determined by a clock in the receiver. A change in the satellite to receiver distance of one wavelength of the GPS carrier (19cm for L1) results in a one cycle change in the phase of the reconstructed carrier.
Relative Bearing The bearing of an object relative to you, with 0° directly in front of you. If you are facing East, with an object to your South, it would have a relative bearing of 90°. An object to the North would have a bearing of 270°.
Relative Navigation A technique similar to relative positioning, except that one or both of the points may be moving. The pilot of a ship or aircraft may need to know position relative to a harbour or runway. A data link is used to relay the error terms to the moving vessel to allow real time navigation.
Relative Positioning The process of determining the relative difference in position between two marks This can be done with a much greater precision than absolute, single point positioning. A receiver (antenna) is placed over each spot and measurements are made by observing the same satellites with each receiver at exactly the same observation interval and with overlapping times . This technique allows the cancellation (during computations) of all errors that are common to both receivers. These include satellite clock errors, propagation delays, etc. See also translocation and differential navigation.
Reliability The probability of performing a specified function without failure under given conditions for a specified period of time.
Repeatable The accuracy with which a user can return to a position whose coordinates have been measured at a previous time with the same navigation system.
RINEX Receiver INdependent EXchange format. A set of standard definitions and formats to promote the free exchange of GPS data and facilitate the use of data from any GPS receiver with any software package. The format includes definitions for three fundamental GPS observables:time, phase, and range. A complete description of the RINEX format is found in the Commission VIII International Co-ordination of Space Techniques for Geodesy and Geodynamics "GPS BULLETIN", May June 1989.
Route Consists of two or more waypoints combined in a course of travel. It provides the automatic capability to navigate through several waypoints, without having to reprogram the unit after arriving at each one. Once programmed into the GPS unit, the route provides the option of navigating forward through the waypoints or in reverse order.
Rover Any mobile GPS receiver collecting data during a field session. The receiver's position can be computed relative to another, stationary GPS receiver.
RSPA Research and Space; Programs Administration (DOT)
RTCM Radio Technical Commission for Maritime Services. A special committee of the commission (Special Committee 104) was set up to define a differential data link to be used to relay GPS correction messages from a monitor (Reference) station to a field user.

RTCM SC-104 recommendations define the correction message format and 16 different correction message types.
RTK Real Time Kinematic. Teal time processing of kinematic data. If the code and carrier data collected at a base station is transmitted in real time to one or more roving receivers, then a computer at the roving receiver calculates the carrier differential processing in real time, results will be available in real time. Such a system is called Real time Kinematic. Although RTCM data formats exist, most manufacturers use proprietary formats.
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