GPS entry terminology and common sense

　　As the best tool for field positioning, GPS is widely used in outdoor sports, and it can be seen more and more often in China. GPS is not like a TV or radio, you can turn it on and use it, it is more like a camera, you need to have a certain amount of knowledge.

　　First of all, we need to clarify some terms that are often encountered when using GPS:

　　1. Coordinate

　　There are 2-dimensional and 3-dimensional coordinate representations. When GPS can receive signals from 4 or more satellites, it can calculate the local 3 micro-coordinates: longitude, latitude, and altitude. If only 3 satellites can be received. signal, it can only calculate 2-dimensional coordinates: precision and latitude, at this time it may also display altitude data, but this data is invalid. Most GPS can not only display coordinates in the form of latitude/longitude (Lat/Long), but also display coordinates in coordinate systems such as UTM (Universal Transverse Mercator), but we generally use the LAT/LONG system. Determined by the coordinate system of the map used. The accuracy of coordinates When Selective Availability (a measure implemented by the US Department of Defense to reduce GPS accuracy) is turned on, the horizontal accuracy of GPS is between 100-50 meters, depending on the number and strength of satellite signals received. , if according to the GPS instructions, you have arrived, then look around, you should find your target in an area about the size of a football field.

　　When SA is turned off, the accuracy can reach about 15 meters. The high accuracy is worse due to the system structure. The display method of latitude and longitude can generally be selected according to your own preferences. Generally, there are "hddd.ddddd", "hddd*mm.mmm", "hddd*mm" ss.s" "" (where "*" represents "degrees" ”, the same below) The earth’s meridian is 39940.67 kilometers long, the latitude changes one degree equals 110.94 kilometers, one minute equals 1.849 kilometers, one second equals 30.8 meters, the equatorial circle is 40075.36 kilometers, the latitude of Beijing is about 40 degrees north latitude, and the latitude circle length is 40075*sin(90-40), the longitude here is 276 kilometers per degree, 1.42 kilometers per second and 23.69 meters, you can select a certain display mode, and change the digits to correspond to how many meters the ground moves to remember, This can establish a rough correspondence between latitude and longitude and actual mileage. Most GPSs have the ability to calculate the distance between two points, giving the exact distance between two coordinates. There are two ways to display the height, the English system and the metric system. Enter the GPS SETUP page and set it to the metric system, so that other displays such as speed and distance will also be in the metric system.

　　2. Landmark or Waypoint

　　The coordinate value of a point stored in GPS memory. When there is a GPS signal, press the "MARK" button, the current point will be recorded as a road mark, it has a default name like "LMK04", you can change it to an easy-to-recognize name (letter Use the up and down arrows to enter), and you can select an icon for it. Road signs are the core of GPS data, which form the basis for "routes" (see 3). Marking road signs is one of the main functions of GPS, but you can also read out the coordinates of a location from the map and enter the GPS manually or through a computer interface to become a road sign. A waypoint can be used in the future for the goal of the GOTO function (see 5.), or it can be selected into a Route, see 3.) as a fulcrum. General GPS can record 500 or more road signs.

　　3. ROUTE

　　A route is a set of data stored in the GPS memory, including the coordinates of a starting point and an ending point, and can also include the coordinates of several intermediate points. The line segment between each two coordinate points is called a "leg". A common GPS can store 20 lines, each with 30 "legs". Each coordinate point can be selected from the existing waypoints, or the values can be entered manually/computer, and the entered waypoints can be saved as a waypoint/Landmark at the same time. In fact, all points of a route are references to a certain waypoint. For example, if you change the name or coordinates of a waypoint under the waypoint menu, if a route uses it, you will find that the same change has occurred in this route. . There can be a route that is "active". The waypoints of the "active" route are the targets of the guidance (see 5) function.

　　4. Forward direction (HeADIng)

　　GPS does not have the function of a compass, and it does not know the direction when stationary. But once it moves, it knows where it's going. The GPS updates the current location information every second. The coordinates of each point can be compared with the coordinates of the previous point to know the direction of travel. Please note that this is not the direction of the GPS head. How many degrees is the movement path at? Different GPS algorithms for heading are different, basically it is the heading of the last few seconds, so unless you have walked for a while and are still walking in a straight line, the heading is not accurate, especially when turning a corner. See the numbers keep changing. The direction is displayed in degrees. This degree is the angle of the watch dial facing up, pointing north at 12 o'clock, and turning clockwise. There are many GPS's that can also show this angle by pointing to a compass and ruler. Generally, the average forward speed is also displayed at the same time, which is also calculated according to the displacement and time of the most recent period.

　　5. Bearing

　　The steering function works under the following conditions:

　　1.) To set a "GOTO" goal. The "Go To" goal can be set by pressing the "GOTO" key and then selecting a waypoint from the list. The "Guide" function will then guide you to this signpost.

　　2.) There is currently an Activity route. Active routes are generally set under the Settings->Routes menu. If there is currently an active route, the "guided" point is the first waypoint in the route, and each time a waypoint is reached, it will automatically point to the next waypoint.

　　In the upper part of the "Guide" page will be marked with the name of the current guidance waypoint (the point in "ROUTE" is also named). It is based on the current position, calculates the direction angle of the guide target to you, and displays it with the same angle value as the "forward direction". At the same time, information such as the distance from the target is displayed. Read the directions and follow this direction to reach your destination. Some GPSs combine the forward direction and the guidance function. As long as the head of the GPS is pointed to the forward direction, there will be a pointer arrow pointing to the declination angle of the forward direction and the target direction, and the target can be found by following this arrow.

　　6. Sun set/raise time

　　Most GPS's can display local sunrise and sunset times, which is useful when planning departure/camp times. This time is calculated by GPS based on the local longitude and date. It refers to the sunrise and sunset time in the plain area. In the mountainous area, because of the ridges, the sunshine time should be less than half an hour in the morning and evening according to the situation. GPS time is Greene time obtained from satellite signals. The local time offset can be set in the setup menu. For China, it should be set to +8 hours. This value is only related to the time display.

　　7. Plot trail

　　GPS updates the coordinate information every second, so it can record its own movement trajectory. General GPS can record more than 1024 footprint points, on a dedicated page, display the moving track with an adjustable scale. The sampling of footprint points has two methods: automatic and timing. Automatic sampling is automatically determined by GPS to determine the sampling method of footprint points. Generally, only the turning point in the direction is recorded, and no points are recorded when walking in a straight line for a long distance; the sampling time interval can be specified for timing sampling, such as 30 seconds. , 1 minute, 5 minutes, or other time, take a footprint point every so long. On the Footstep Lines page you can clearly see the horizontal projection of your footsteps. You can start recording, stop recording, set the way or clear the footprint. The points on the "footprint" line have no names and cannot be referenced individually. To view their coordinates, they are mainly used to draw a route map (computer download route?) and the "backtracking" function. Many GPS have a function called "Trace back". When using this function, it will convert the footprint line into a "route" (ROUTE). The selection of waypoints is completed by the internal program of the GPS. Generally, the footprint is selected. Big turning point online.

　　At the same time, if this route is activated as an active route, the user can return to the original route according to the guidance function. It should be noted that the backtracking function generally puts the backtracking route into a default route (such as route0), see the manual of your GPS, and check whether the route has data before using it. If there is, use the copy function to copy it first. to another empty line to avoid overwriting. The waypoints on the backtracking route use the default temporary names of the system, such as "T001", and some GPS will reuse these names when setting the second backtracking route. At this time, even if you have copied the old route, because the road The name of the point reference is reused, so the route will also change, not the original backtracking route. Please check the instruction manual of your GPS and try it out to clarify your situation. If necessary, for the TraceBack route that needs to be saved for a long time, copy it to the idle route and rename all the waypoint names

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