Satellite navigation knowledge (middle)

5. How to use the GPS receiver (1)

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As the best tool for field positioning, GPS has a wide range of applications in outdoor sports, and people can be seen more and more frequently in China. GPS is not like TV or radio. It can be used when it is turned on. It is more like a camera. You need to have some skills. Now introduce some GPS usage methods and experience.

First of all, you have to figure out some terms that you often encounter when using GPS:


There are two-dimensional and three-dimensional coordinates. When the GPS can receive signals from four or more satellites, it can calculate the local 3 micro-coordinates: longitude, latitude, altitude. If only three satellites are received. Signal, which can only calculate 2D coordinates: precision and latitude, at which point it may also display height data, but this data is invalid. Most GPS can display coordinates not only in Lat/Long, but also in coordinate systems such as UTM (Universal Transverse Mercator). But we usually use LAT/LONG system, which is mainly for you. The coordinate system of the map used is determined. The accuracy of the coordinates is turned on when Selective Availability (a measure implemented by the US Department of Defense to reduce GPS accuracy). The horizontal accuracy of the GPS is between 100 and 50 meters, depending on how much and how strong the satellite signal is. If you have arrived according to the GPS instructions, then look around and you should find your target within about the size of a football field.

When the SA is closed (the US government has cancelled the SA), the accuracy can reach about 15 meters. The high degree of accuracy is even worse due to the structure of the system. The display 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 "*" stands for "degree" "The same as below" the Earth meridian length is 39940.67 kilometers, the latitude change is 110.94 kilometers, one point is 1.849 kilometers, one second is 30.8 meters, the equatorial circle is 40075.36 kilometers, the Beijing area is about 40 degrees north latitude, and the latitude circle is 40075*sin(90-40), the longitude of this place is 276 kilometers, one point is 1.42 kilometers and the second is 23.69 meters. You can select a display mode and change the number of each digit to the ground. This creates a rough correspondence between latitude and longitude and actual mileage. Most GPSs have the ability to calculate two points of distance, giving the exact distance between two coordinates. The height display will be in English and metric. Enter the GPS SETUP page and set it to metric, so that other displays such as speed and distance will be metric.

2. Landmark or Waypoint

The coordinate value of a point saved in the GPS memory. When there is a GPS signal, press the "MARK" button, it will record the current point as a road sign. It has a default name like "LMK04". You can change it to a recognizable name (letter). Use the up and down arrows to enter) and you can also select an icon for it. The road sign is the core of the GPS data, which is the basis for the “route” (see 3). Marking road signs is one of the main functions of GPS, but you can also read the coordinates of a place from the map and enter GPS by hand or through a computer interface to become a road sign. A road sign can be used for future GOTO functions (see 5), or you can choose a route Route, see 3.) as a fulcrum. Generally, GPS can record 500 or more road signs.

3. Route (ROUTE)

A route is a set of data stored in GPS memory, including the coordinates of a starting point and an ending point. It can also include the coordinates of several intermediate points. The line segment between each two coordinate points is called a "leg". Common GPS can store 20 lines, 30 "legs" per line. Each coordinate point can be selected from existing road signs, or manually/computer input values, and the input waypoints are simultaneously saved as a road sign (Waypoint/Landmark). In fact, all points of a route are references to a road sign. For example, if you change the name or coordinates of a road sign under the road sign menu, if a route uses it, you will find that the same change has occurred in this route. . There can be one route that is "Active". The waypoints for "active" routes are the goals of the guided (see 5) function.

4. Heading direction (Heading)

GPS does not have the function of a compass, and it does not know the direction when it is stationary. But once it moves, it can know where it is moving. The GPS updates the current location information every second. The coordinates of each point are compared with the coordinates of the previous point. You can know the direction of the advance. Please note that this is not the direction of the GPS head. It does not know the head and the old man. How many degrees of angle the movement route is. Different GPS algorithms for heading are different, basically the direction of the last few seconds, so unless you have gone a long way and are still in a straight line, the direction is not accurate, especially when you turn See that the value is changing. The direction is shown in degrees. The degree is that the watch dial is facing up, 12 points to the north, and the angle is clockwise. There are many GPSs that can also display this angle by pointing to the compass and the ruler. Generally, the forward average speed is also displayed, which is also calculated based on the displacement and time of the most recent period.

5. Guide (Bearing)

The steering function works under the following conditions:

1.) Set the "going" (GOTO) target. To set the "going" target, press the "GOTO" button and select a road sign from the list. Later "steering" functions will lead to this road sign.

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

The current guide point name is also marked on the top of the "Guide" page (the point in "ROUTE" is also named). It calculates the direction angle of the guiding target against you based on the current position, and displays it at the same angle value as the "forward direction". Also displays information such as the distance from the target. Read the direction of the guide and advance in this direction to go to the destination. Some GPS combines the forward direction and the guiding function. As long as the head of the GPS is pointing in the forward direction, there will be a pointer arrow pointing to the yaw angle of the forward direction and the target direction, and the arrow can be used to find the target.

6.Sunset/raise time

Most GPS can display local sunrise and sunset times, which is useful when planning departure/capping time. This time is calculated by GPS according to the local longitude and date. It refers to the sunrise and sunset time in the plain area. Because of the ridges in the mountains, the sunshine time is less than half an hour according to the situation. The GPS time is the Gurney time obtained from the satellite signal. 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 display of time.

7. Footline (Plot trail)

The GPS updates the coordinate information once per second, so you can record your own motion trajectory. Generally, GPS can record more than 1024 footsteps, and on a dedicated page, the movement track is displayed with an adjustable scale. The sampling of the footsteps has automatic and timed automatic sampling. The sampling method of the footsteps is automatically determined by the GPS. Generally, only the direction turning points are recorded, and the long distance straight lines are not recorded; the timing sampling can specify the sampling time interval, for example, 30 seconds. One minute, five minutes or other time, record a foothold every so long. The horizontal projection of your footprint can be clearly seen on the Footprints page. You can start recording, stop recording, set up, or clear the footsteps. The points on the "footprint" line have no name, can not be quoted separately, view their coordinates, mainly used to draw the road map (computer download route?) and "backtracking" function. Many GPSs have a feature called "Trace back". When you use this function, it converts the footsteps into a "route" (ROUTE). The choice of waypoints is done by the GPS internal program. A big turning point on the line. At the same time, the route is activated as the active route, and the user can return by the guiding function. It should be noted that the backtracking function generally puts the backtracking route into a default route (such as route0). Look at your GPS manual. Before using it, check whether the line has data. If so, copy it first. Go to another empty line to avoid overwriting. Each waypoint on the backtracking route uses the system's default temporary name such as "T001", and some GPS will reuse these names when setting the second backtracking route. Even if you have already copied the old route, due to the road The name of the point reference is reused, so the route will change, not the original backtracking route. Please check your GPS instruction manual and try to clarify your situation. If necessary, copy the TraceBack route that needs long-term storage to the free route and rename all waypoint names.

6. How to use the GPS receiver (2)

GPS compares the battery, most GPS uses four alkaline batteries and can be turned on for 20-30 hours. The time on the manual is not very accurate. Please pay attention to carry the spare battery when using for a long time. Most GPS have a permanent backup battery that ensures that all data in the memory is not lost when there is no battery. Since the GPS has no direction indication function when it is stationary, it is useful to bring a small north arrow at the same time. When marking road signs, GPS provides a default road sign name, such as LMK001, which is difficult to remember. Although it can be changed to a better name, but the input is inconvenient, it is very difficult to use the up and down arrows to select letters, and the second is generally only It is a good idea to be able to record a short English name, such as 6 or 9 letters, which is still not easy to remember, and then take a small tape recorder/interview machine to record at any time.

1. Use maps

GPS has the best effect when used in conjunction with detailed maps, but domestic large-scale maps are very rare, and GPS usage is limited. If you have an accurate map near your destination, you can plan the route in advance, plan on the map, make a trip plan, and create one or more lines (ROUTE) according to the complexity and mileage of the line. For the coordinates of the route feature points, enter the GPS "legs" to establish the line, and enter some individual marker points as landmarks (Landmark/Waypoint) into the GPS. GPS manual input of data is a rather cumbersome thing. Please think that each road sign should enter more than 20 alphanumeric characters such as name and coordinates. Each alphanumeric character can be pressed up to a dozen or so times to come out, haha, This is why someone is willing to spend a lot of money on wiring and software to upload/download data using a computer. Bring a map! The first one is to use GPS to determine the position of the map on the map. The second is to follow the direction indicated by the guiding function and find the way to the target. At the same time, it is necessary to record the actual coordinates of each planning point. It is better to establish another actual line for each planned line, which can be used as the original road return, and can be saved as the actual route data for later generations.

2. No picture use This is a more common way to use it.

1.) Use waypoint fixed point: It is often used to determine the rock wall coordinates, determine the hole coordinates or other coordinates like the starting point, turning point and camping point of the line when exploring the hole. Simple to use, MARK a coordinate will do. Find a point: the coordinates of the location you are looking for must already exist in the GPS memory in the form of a landmark/waypoint. It can be your previous MARK point or data obtained from a friend you have been to before, manual/computer upload. Road sign data. Press the GOTO button, select your destination roadmap from the list, and then go to the “Guide” page, which will display the distance, speed, target direction angle and other data from the target, according to the direction angle.

2.) Use the route to enter the route: If you can find the route information recorded by the friends you have been to before, enter them into the GPS to form the route, or (commonly on the original route to return) the previously recorded road signs into a line. Route Orientation: Activate a route. In the same way as “find the point”, the “Guide” page will guide you to the first point of the route. Once it arrives, the target point will be automatically replaced with the next waypoint. The page guides you to the second point of the route... If you deviate from the route and cross some intermediate points, once you return to the route, the "guided goal" will skip the points you have bypassed. Is the next point on the line that corresponds to your current location.

3.) The backtracking backtracking function is actually a special method of inputting a route, which is very good when returning from the original path. But there are some considerations,

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