Handling of the GPS

Today, technology has become part of our mountain and trekking activities, helping us, for example, to know and share our location in a quick, simple and exact way, providing us with greater security on the routes and giving us data and information with hardly any technical knowledge. GPS devices and applications that turn our cell phone or tablet into an advanced navigation system. It is important to know how to use them and how they work so that, if necessary, we have correct data to help us solve the situation in which we find ourselves.

• In mountain and trekking activities we should always carry a map of the area and a compass, we should not trust 100% of the orientation of the route in the GPS or in the mobile, since these can have limitations that prevent them from working properly.
• It goes without saying that at the beginning of the tour the batteries or piles must be at their maximum capacity, in addition we must carry piles or spare batteries.
• Preparing the route in advance will avoid unpleasant surprises. Look for a correct track of the route, check it and install it in your GPS, it's also not a bad idea to record some WPTs with the important places of the route.
• Do not expect precision to the millimeter, fortunately technology advances rapidly and every day improves the precision of the civil devices we use, however a precision that ranges between 2 and 14 m can be considered normal. There are many factors that can influence the inaccuracy of our device.

• Familiarize yourself with the operation of the device in a familiar environment and without the pressure of an uncontrolled situation during a tour, this will allow us to perform all the necessary tests to expand our knowledge.
• Start from scratch each route, although the memory and processing capacity of the devices we can find in the market is increasing every day, it is still advisable not to load it with unnecessary data from other routes that are not even in the area where we are.
• Before starting a route set the track log to 0% to avoid, among other things, that it is completed in the middle of a route, it is also advisable to reset the counters for navigation, distance traveled, speed, etc.
• Don't let it sound strange, UTM coordinates, Datum, etc... are terms that are part of the navigation with GPS, in addition most of the topographic maps used in hiking and mountain are drawn having these values as reference.

The Global Position System allows a hiker or mountaineer to know at all times and with great accuracy his position, to go to any point where he knows his coordinates or follow a certain route through his GPS device. This system, developed in the early 70's for war purposes, has become a public system used by millions of people around the world, and knowing its basic operation and limitations will be of great help to us on our routes.

GPS obtains our position by receiving a series of radio signals emitted by a network of satellites orbiting the earth at a given distance. There are several different satellite systems such as NAVSTAR or GLONASS.

To calculate our position and height it is necessary to have at least the signal of 4 satellites that serve to know the distance that separates us from them so that the GPS can triangulate our location.

There are a number of factors that affect the accuracy of the location shown by the device:

• The number and quality of signals received.
• The speed of the signal, the greater the electrical charge in the atmosphere or the greater the inclination of the satellite compared to the vertical sample, the worse the accuracy will be.
• Obstacles where the signal could bounce, buildings, mountain walls...
• Orbital mismatches or modifications of the satellites.
• Thick forests and wet tree leaves.

The data of our position are georeference coordinates that the GPS shows, so we must master some basic concepts of mapping and orientation. Our GPS can show us the data of position in different formats (DDºMM'MMM'', MGRS, UTM, etc...) the model of projection of the cartography used in Spain and more advisable for the outdoor is the UTM (Universal Transversal Mercator).

This system divides the earth plane into squares by means of transversal and longitudinal bands, which gives us a total of 60 spindles and 20 transversal bands identified from C to X. The Iberian Peninsula is positioned between spindles 29, 30 and 31, and bands S and T.

As a general rule, any topographic map that includes the UTM kilometer grid will also provide us with the spindle, so we will only have to obtain the X and Y coordinates corresponding to the equator and the meridian respectively but from the grid we are on. From there the format of these coordinates 30T (spindle and band) 512733 (X distance from the equator) 4649628 (Y distance from the meridian).

It is important to know that the coordinates are always subject to a DATUM, which takes into account the irregularities of the earth's surface in each region.

Until relatively recently the reference DATUM was EUR 50 but this has been replaced by the ETRS 89 which covers the whole of the European Union. It happens that in many GPS models this DATUM does not appear, we do not have to worry because the WGS84 is the same as the ETRS 89, with minimal differences that in the normal use that we are going to make we will not appreciate.

It is tremendously important to configure this section of our GPS and position it in the DATUM of the map that we have loaded on it, because if we do not we can find differences of more or less 200 m with the real location in which we are.

• Navigation by fixed course, in which we select a point of interest or a place on the map to which we want to go and the GPS will always draw a straight line from our location to the selected place or set the course on the GPS compass indicating the orientation of the destination with respect to us. This system requires more knowledge in orientation since between us and the place we want to go there may be an obstacle (a ravine, a mountain cliff...) that gets in our way making it impossible to reach the place where the GPS marks the straight line, forcing us to interpret the map to choose the best route.
• Navigation by route or track, in this case we must have a track or route already entered in the memory of our device to order it to lead us following this pre-established route to the point we choose from it. This system, known as Track Back is very similar to the GPS of cars that tell us when we should deviate and what route we should follow.

• Check well at home the track you download, not all are reliable and some are not updated.
• Before starting the route, create a start waypoint to which you can return in case of problems. They are usually created independently of the tracks and if these are accidentally deleted we will always know where we have to go.
• Make sure you have your Track Log activated so that your GPS leaves its own breadcrumbs, that is, creating its own route. No matter how good your track is from home, you can get confused and go a long way until you realize your mistake, so you always make sure you have marked the route you followed and you can go back to the point where you turned off without any major complications.
• It is advisable to create points of interest that indicate crossings or places that may be important on the route. A shelter to which we do not give importance and through which we pass with good weather can be a very pleasant place if we are surprised by a storm.