C/A Code
See Coarse/Acquisition Code Cache Memory
Cache memory is random access memory (RAM) that a computer microprocessor can access more quickly than it can access regular RAM. Carrier
A steadily transmitted RF signal (radio wave) whose amplitude, frequency or phase (or a combination) may be modulated from a known reference to carry information. Carrier-Aided Tracking
A method to improve accuracy by using the GPS carrier signal to get a more precise lock on the pseudorandom (PRN) code. Carrier Frequency
The frequency of an unmodulated output of a radio transmitter. The GPS L1 carrier frequency is 1575.42 MHz. Carrier-Tracking Loop
A module in a GPS receiver that demodulates, or extracts, the satellite message by aligning the phase of the receiver's local Oscillator">oscillator signal with the phase of the frequency-shifted, received carrier.
Once the local Oscillator">oscillator signal is locked to the carrier, its phase can be measured to provide the carrier-phase observation. Cartography
The art or technique of making maps or charts. Many GPS receivers have detailed mapping – or cartography – capabilities. CCD
A digital camera is very much like a camcorder. Rather than focusing the image of the scene you wish to record on film, a digital camera focuses the image onto a light-sensitive chip (CCD) which in TRN)+">turn converts the image into digital form. CDI
See Course Deviation Indicator CDMA
See Code Division Multiple Access CEP
See Circular Error Probable CF card
See Compact Flash card Channel
A channel of a GPS receiver consists of the circuitry necessary to receive the signal from a single GPS satellite. Chip
Binary elements or digits that, unlike bits, convey no information. A PRN code consists of a sequence of chips. Chip Rate
The number of chips sent per second. Chartplotter
A device that overlays GPS data on to marine navigational charts. Circular Error Probable (CEP)
The radius of a circle within which fifty percent of positioning solutions fall. CEP is used to achieve horizontal accuracy. Clinometer
A device, usually similar to a compass, used to measure vertical angles, as in the slope of a hill. Clock Aiding
An accuracy enhancement technique in which an additional atomic clock (rubidium) provides accurate time to the receiver for calculating satellite clock frequency, phase bias, and clock bias. Clock Bias
The difference between the indicated clock time in the GPS receiver and true universal time (or GPS satellite time). CMG
See Course Made Good Coarse/Acquisition Code (C/A Code)
Also known as the Civilian Code or S-Code. The standard positioning signal the GPS satellite transmits to the civilian user. A sequence of 1023 pseudo-random, binary, biphase modulations on the GPS carrier at a chip rate of 1.023 MHz. It contains the information the GPS receiver uses to fix its position and time, and is accurate to 100 metres or better. Code Division Multiple Access (CDMA)
A method of frequency sharing where many transmitters use the same frequency but each one has a unique code to generate pseudorandom sequences. GPS uses CDMA with Gold codes. Code-Tracking Loop
A module in a GPS receiver used to align a PRN code sequence present in a signal coming from a satellite with an identical PRN code sequence generated within the receiver. Alignment is achieved by appropriately shifting the receiver-generated code chips in time so that a particular chip in the sequence is generated at the same instant its twin arrives. COG
See Course Over Ground Cold Start
Used to describe state where a GPS receiver is powered on and does not have valid almanac data available. This lengthens the time required to locate satellites and arrive at the first position solution. COM Ports
The connectors and accompanying circuitry that allow serial devices (usually serial printers, modems, or mice) to be connected to PC. Communication ports are also called serial ports. To keep track of the devices, DOS assigns names that begin with the letters COM to communication ports (such as COM1 and COM2). Commercial Software
Software that must be purchased before use. There is no “testing” period available before the customer must spend money for the product. Communications Port
Connects your PDA to its cradle (or to an optional USB or serial cable) Compact Flash card (CF card)
Cards that can be used in small devices like handhelds. They can be used for storage (memory) or to accept removable accessories such as additional memory or GPS receivers. Constellation
Refers to either the specific set of satellites used in calculating a position, or all the satellites visible to a GPS receiver at one time, or the entire ensemble of GPS satellites comprising the Space Segment. Control Point
Also called a control station. Locations on the earth's surface used for mapping references. Can be horizontal or vertical or both. Often these are bench marks. Control Segment
A worldwide chain of monitoring and control points that control and manage the GPS satellite constellation. Control Station
See Control Point Contour interval
The difference, in feet or meters, in elevation between two adjacent contour lines. Contour line
A line on a topographic map that represents a specific elevation. Coordinates
A set of numbers that represents a precise location anywhere on Earth. Usually stated as latitude and longitude. Coordinated Universal Time (UTC)
Replaced Greenwich Mean Time (GMT) as the world standard for time in 1986. UTC uses atomic clock measurements to add or omit leap seconds each year to compensate for changes in the rotation of the earth. Course
The direction from the beginning landmark of a course to its destination (measured in degrees, radians, or mils), or the direction from a route waypoint to the next waypoint in the leg. Course Deviation Indicator (CDI)
A technique for displaying the amount and direction of crosstrack error (XTE). Course Made Good (CMG)
The bearing from your starting point to your present position. Commonly used in marine or air navigation. Course Over Ground (COG)
Your direction of movement relative to a ground position. Course To Steer
The heading you need to maintain in order to reach a destination. Course Up Orientation
Fixes the GPS receiver's map display so the direction of navigation is always “up” Cradle (USB/Serial)
This holds your PDA and acts as a communication conduit between the PDA and the computer. You can synchronize data and download programs from the PC. Some cradles double as battery chargers. USB and Serial are the types of ports on the computer to which you attach the cradle. Crosstrack Error (XTE/XTK)
The distance you are off a desired course in either direction. Cut-off Angle
The minimum acceptable satellite elevation angle (above the horizon) to avoid blockage of line-of-sight, multipath errors or high Tropospheric or Ionospheric Delay values. May be preset in the receiver, or applied during data post-processing. For navigation receivers may be set as low as 5°, while for GPS Surveying typically a cut-off angle of 15° is used. Cycle Slip
If a GPS receiver loses a signal temporarily, due to obstructions for example, when the signal is reacquired there may be a jump in the integer part of the carrier-phase measurement due to the receiver incorrectly predicting the elapsed number of cycles between signal loss and reacquisition. |
