Author Topic: Humminbird Glossary - GPS & Navigation Terms  (Read 21110 times)

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Offline RGecy

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Humminbird Glossary - GPS & Navigation Terms
« on: May 21, 2009, 11:02:19 PM »
Glossary – GPS and Navigation Terms

Acquisition Time: The length of time that a GPS receiver typically takes to determine a position from at least three satellites. Humminbird® GPS receivers provide very fast acquisition times (under one minute), permitting users to get out on the water faster.

Alarm, Arrival: The audible alert that sounds when the boat is equal to or less than the alarm setting (25 feet – 3000 feet) from the location of the destination waypoint.

Alarm, Drift: Drift Alarm is an audible alert that sounds when the boat is equal to or over the alarm setting (25 feet – 3000 feet) from the location where the alarm was turned on.

Alarm, Off-Course: Off-Course Alarm is an audible alert that sounds when the boat’s distance from the intended Track, (Cross Track Error), is equal to or over the alarm setting (25 feet – 3000 feet). See Track and Cross Track Error.

Altitude: Altitude measures height above sea level. Altitude is a measurement that can be provided by GPS.

Bearing (BRG): Bearing is the direction to a destination waypoint measured in degrees from North (i.e. 321°, where 000° is North, 090° East, 180° is South, 270° is West).

Chartplotter: Chartplotter describes a navigation device that shows Present Position on a Map, along with Tracks, Waypoints, and Routes. All Chartplotters are also considered Trackplotters. All Humminbird® GPS Combo units are Chartplotters. See Trackplotter.

Cold Start: Cold Start refers to the procedure that a GPS receiver must perform when it does not have historical information regarding its current location. This procedure typically lasts for several minutes, and may be experienced upon first power up of the receiver, or if the receiver has been moved a great distance.

Course Over Ground (COG): Course Over Ground is the current direction the boat is traveling measured in degrees from North (i.e. 321°, where 000° is North, 090° East, 180° is South, 270° is West). When the Course Over Ground is equal to Bearing, the boat is said to be “On Course” and will arrive at the destination in the most efficient manner. COG is often confused with Heading. See Heading.

Cross Track Error (XTE): Cross Track Error is the straight-line distance of the boat from the intended Track. XTE measures how far the boat is off course, and also triggers the Off Course Alarm. See Track.

Differential GPS (DGPS): Differential GPS is a system to improve the position accuracy of the Department of Defense GPS through the use of secondary “correction signals” broadcast from ground stations around the coastal United States and on some inland waterways. These correction signals are provided by the USCG and received by an auxiliary Differential Beacon Receiver (DBR) that connects to the GPS receiver. The advent of WAAS has largely negated the need for the added expense of a DBR in the United States.

Distance To Go: Distance To Go is the straight-line distance between Present Position and the Destination Waypoint. DTG and SOG (Speed Over Ground) are used to calculate Time To Go. See Time to Go and Speed Over Ground.

Estimated Position Error (EPE): Estimated Position Error is a calculation that indicates the potential position inaccuracy the user may experience due to a variety of GPS factors which include satellite position in the sky, signal strength and others factors.

Fix Type: Fix Type indicates whether the GPS receiver is providing 2D fix or 3D fix. A 2D fix requires only three satellites and provides only latitude and longitude. A 3D fix requires four or more satellites, and provides latitude, longitude and altitude.

GPS: GPS is an acronym for Global Positioning System. GPS provides accurate position (latitude, longitude, altitude) information virtually anywhere on the earth through satellite technology and personal receivers on the ground. A series of geosynchronous satellites broadcast a unique signal toward the earth once per second. A GPS receiver, such as that included with many Humminbird® products, receives the signals from these satellites and is able to determine position based on very slight differences in the time each signal is received and the receiver’s knowledge of the location of each of the satellites.

Heading: Heading describes the direction the boat is pointing and is measured in degrees (i.e. 321°, where 000° is North, 090° East, 180° is South, 270° is West). Due to wind and waves, the boat is often traveling in a slightly different direction than it is heading, and therefore Heading is often confused with Course Over Ground. See Course Over Ground.

Map Datum: A Map Datum refers to a particular survey of the earth’s surface that was referenced when creating a chart (i.e. WGS84). Since the earth is not flat, and not even consistently round, a mathematical model must be used to translate coordinates from the sphere of the earth to the flat surface of a chart. This mathematical model is the Map Datum. Historically, many different Map Datums have been used around the world to create maps; often a reference to the Map Datum can be found in the legend of a paper map. It is important to select the correct Map Datum setting in your fishfinder when comparing GPS position to a paper chart to avoid slight position inaccuracies. Almost all electronic charts use the WGS84 Map Datum and therefore, they do not require setting changes.

MMC: MMC is an acronym for Multi Media Card. An MMC is a postage stampsized memory device used to store electronic data such a maps, waypoints, routes and other information. MMC is a very rugged format suitable for the marine environment, but it is not waterproof. The MMC is removable from Humminbird® products, and can be used in a PC that is equipped with an appropriate card reader. MMC is the same format that many digital cameras use. See SD.

North, Magnetic: North is the principle reference point of the compass (i.e. North is 000°). Magnetic North relies on the earth’s magnetic field to align a metal pointer generally towards True North. However, due to local variations in the earth’s magnetic field around the globe, the difference between True North and Magnetic North can be greater than 10°. See True North.

North, True: North is the principle reference point of the compass (i.e. North is 000°). True North uses the axis of the rotation of the earth as the reference for North and is constant for all points on the earth. Most GPS units default to True North as the setting. The GPS heading may vary from the boat compass heading because the compass uses Magnetic North. Humminbird® GPS units provide the option of selecting True or Magnetic readouts by using the North Reference menu. See Magnetic North.

Present Position: Present Position is the current location (latitude, longitude) determined by GPS. The Present Position is indicated on-screen by a directional boat icon if the boat is moving, or a round symbol if the boat is stationary.

Route: A Route is series of waypoints linked together in a specific sequence to define a navigation path between two points, and saved in the fishfinder’s memory. Routes are often used when frequently traveling between two or more locations because it is a faster and more accurate method than repeatedly selecting individual waypoints each time one travels through the same area. Routes consist of a Start Waypoint, an End Waypoint, and a series of waypoints in between. Users can begin navigation at the beginning, the end (to run the route in reverse) or at any waypoint in between. See Waypoint.

SD: SD is an acronym for Secure Digital. An SD card is virtually identical in function to an MMC; however, the speed at which information can be accessed is generally faster, the storage capacity is generally larger, and the card has security features which can be used to prevent extracting the data from the card. SD is the same format that many digital cameras use. See MMC.

Selective Availability: Selective Availability (SA) is a GPS system “feature” that can be implemented by the U.S. Department of Defense (DoD) to degrade the accuracy of GPS positioning information. With SA active, the GPS is accurate to within 100 meters 95% of the time. With SA inactive, the GPS is accurate to within 45 meters 95% of the time. Currently, SA is inactive and the consumer can enjoy the greater precision GPS provides; however, the DoD reserves the right to activate SA at any time.

Speed Over Ground (SOG): Speed Over Ground is the measurement of the boat’s progress across a given distance, and is the speed measurement provided by GPS. An alternate, Speed Through Water, is provided by a speed paddlewheel, and is the measurement of the flow past the boat, which may vary depending on current speed and direction. Speed Over Ground is optimal for navigation because accurate destination times can be derived from this measurement. Humminbird® products allow for input and display of both speed measurements.

Time To Go (TTG): Time To Go is the estimated time required to reach the destination waypoint. TTG is calculated using the SOG and DTG. See SOG and DTG.

Track: A Track is a series of saved points that define the past path of the boat. These Track Points are saved at regular time intervals. Tracks are a useful and quick method to see where you’ve been, and an easy guide to follow to get you back to the starting point. Generally, all GPS units have a limited number of Track Points that can be saved before the unit runs out of memory and begins erasing the first track points saved. Because of this, the user can adjust the Track Point Interval menu to increase the amount of time between when points are saved, and thus extend the distance covered by a track. Tracks can also be permanently saved to memory, and re-displayed at the user’s option.

Track Line (TRK): The Track Line is the desired line of travel between two waypoints, and represents the most efficient path between the two points because it is a straight line. The TRK is measured in degrees (i.e. 321°, where 000° is North, 090° East, 180° is South, 270° is West). See Cross Track Error and Course Over Ground.

Trackplotter: Trackplotter describes a navigation device that shows Present Position, along with Track, Waypoint, and Routes, but NO MAP in the background. See Chartplotter.

Trolling Grid: Trolling Grid is a Humminbird® feature that displays a precise reference grid around a waypoint. This grid is used as a guide pattern for trolling around a specific area to assure a more efficient and complete coverage of that area. Trolling Grid resolution be changed by zooming in or out on the chart. The Trolling Grid can also be rotated on the display to orient it for optimal boat course for wave and wind conditions.

UTC: UTC is an acronym for Universal Time Constant. UTC is the “standard time” used in navigation, and is the local time in Greenwich England. (UTC is equivalent to Greenwich Mean Time (GMT)). To display the correct Local Time in a Humminbird® GPS unit, the user must use the Local Time Zone menu and select the time zone (i.e. EST, CST).

WAAS: WAAS is an acronym for Wide Area Augmentation System. WAAS is complementary technology to GPS that provides enhanced accuracy through correction signals broadcast from Federal Aviation Administration WAAS satellites stationed over the USA. These secondary signals are automatically received by the standard Humminbird® GPS Receiver. With WAAS signal, GPS accuracy is improved to within 3 meters 95% of the time. Outside the United States, regional governmental coalitions have created similar systems such as EGNOS (Europe) and MSAS (Japan).

Waypoint: A Waypoint is the saved location (latitude, longitude) of a point of interest that is stored in a GPS receiver’s memory. This can include a marker buoy, dock, fishing hole or anywhere else the user may want to return to. Humminbird® products offer the ability to name and assign a symbol to the saved location. Depth, Date and Time of Day when the waypoint was created is also saved.

Waypoint Target: Waypoint Target is a Humminbird® feature that displays a precise “bull’s eye” around a selected waypoint. This bull’s eye is used to easily monitor boat position relative to a waypoint, and is useful for fishing over submerged structure. With Waypoint Targets, a quick look at the screen lets you know how far off the waypoint the boat has drifted.
« Last Edit: May 23, 2009, 03:56:16 PM by RGecy »
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