*  Authenticity

Authenticity is the first trail-running value. At its origins, trail-running was born from the runners’ motivation to practise their sport in contact with natural surroundings, so as to experience the beauty of the landscape and to learn to evolve without artifice in an environment that is demanding for both body and spirit. Trail-running is an authentic sport, because it creates a confrontation between the participant and the unspoilt natural environment as a source of inspiration, surpassing oneself, but also one of harmony.

As a social activity, trail running promotes human relationships based on simplicity, conviviality, sharing and respect for differences. The trail-running community gives these authentic values as much importance as those of performance and competition.

How to measure a race

Measuring a race

The Trail Race agenda is growing every year, and so is participation in each race. To create better races, it is essential to have better organizations. Thus each race organizer should pay attention to every essential element.

Among others, one of the main aspects of any race is the information to runners and, among them, the correct distances and elevations.
Elite runners are performing at the edge of their limits so a precise information will allow them to elaborate the best strategy for their performance. Poor or imprecise information could lead to a bad result or to directly abandon a race. For the rest of the runners, even if they may not be performing on as high a level as an elite; their limits are normally lower so the previous reason is also applicable. Anyway giving accurate information is a matter of seriousness of any so-called organization.

Technilogy

Trail races are, as we know by now, undertaken in a natural environment, out of roads and towns where elevation gain and loss is a normal factor. Dust roads, single tracks or grass fields are common and finding obstacles such as mud, rocks, roots is a habit. So trying to use any of the known measuring devices used in a road races such as calibrated bicycle is an absolute non-sense.

The only option is to use any method that doesn’t need a wheel to follow the race and, for now, the best option is using GPS Technology.

GPS (Global Positioning System) encompasses three segments: space, control, and user. Space segment is a system of 24 NAVSTAR satellites in earth orbit around 20.000km high. Each satellite contains several high-precision atomic clocks that constantly transmits radio signals using a unique identifying code.

The Control segment is formed by five monitor stations and ground antennas spread all over the earth and all the receivers (our personal GPS units) are the last segment: the user segment.

The system is owned by US government and managed by Department of Defense. GPS works in any weather conditions, anywhere in the world, 24 hours a day. There are no subscription fees or setup charges to use GPS.

In addition to US GPS, other systems are in use or under development although almost all are limited, for the moment, to regional coverage.

  • The Russian Global Navigation Satellite System (GLONASS) was developed contemporarily with GPS, with yet incomplete coverage of the globe.
  • GALILEO a global system from  the European Union
  • BEIDOU and COMPASS, Chinese navigation systems
  • IRNSS, Indian Regional Navigational Satellite System
  • QZSS from Japan.

How does a GPS work?

Each satellite processes two types of data, Ephemeris, that is its exact position in space and time in UTM (Universal Time Coordinated). The second data is the Almanac; the same data as the Ephemeris but related to other satellites in the network as well as their orbits. Each one sends all this information constantly to the Earth using radio signals.

When we turn on our unit it starts getting these signals from all visible satellites (GPS devices do not send any radio signal, they are receivers) starting with the strongest one and continuing with the rest.

Once the receiver has at least three satellites in sight, and knowing the distance to all three, it can calculate our position on the Earth’s surface. This position is called Longitude and Latitude. With a fourth satellite the precision is higher and also elevation data can be calculated.

Data precision

Originally GPS technology was created for military purposes, so the precision is quite high. From 1980, the system was open to civilian use and the US government included a random error called SA (Selective Availability) to eventually limit this precision. This error was cancelled from the system in May 2000 when Bill Clinton was president.

Besides the SA error, a GPS signal can have different types of errors due to clock drift, ephemera, or ionosphere delay, some of these error can be partly corrected, some not.

Integrating external information into the calculation process can materially improve accuracy. The normal error for any GPS with standard use could be around 15 meters. Another system called DGPS (Differential GPS), allows the GPS signal to be corrected by a secondary signal emitted by a fixed position on Earth, can increase this precision up to 1 meter.

Other examples of augmentation systems include the Wide Area Augmentation System (WAAS), European Geostationary Navigation Overlay Service (EGNOS), Differential GPS, Inertial Navigation Systems (INS) and Assisted GPS.

Considering all this, GPS technology is, according to us, the best option for measuring a trail race.

Some Limitations

GPS can provide worldwide, three-dimensional positions, 24 hours a day, in any type of weather. However, the system does have some limitations:

  • There must be a relatively clear "line of sight" between the GPS antenna and four or more satellites to be able to obtain a good confirmed position.
  • Objects, such as buildings, overpasses, and other obstructions, that shield the antenna from a satellite can potentially weaken a satellite's signal such that it becomes too difficult to ensure reliable positioning.
  • Signal Bouncing: these difficulties are particularly prevalent in urban areas. The GPS signal may bounce off nearby objects causing another problem called multipath interference.

Elevation with a GPS

GPS heights are based on an ellipsoid, a mathematical representation of the Earth's shape, more or less accurate, but not precise, while map elevations are based on a vertical datum tied to the geoid (or what is commonly called: “sea level”). 
Basically, they are two different systems, although they have a relationship, that have been combined.

The main source of error has to do with the arrangement of the satellite configurations during fix determinations. Once the vertical datum is taken into account, the accuracy permitted by geometry and mathematical considerations remains less than that of horizontal positions.

It is not uncommon for satellite heights to be off from map elevations by +/- 150m.

The only option to have a better reading for altitude is to have a GPS unit with barometric sensor, and to adjust it before starting.

Barometric sensor overlaps information on the registered information and will give, if the weather doesn’t change much, a more precise data track than using the ellipsoid.

Measuring a race

Considering the pros and cons of GPS technology, there are some recommendations that we give to ensure the best result.

Data Registering

  • Chose a clear day. Although GPS signal works in any weather, thick clouds could create some lack of precision.
  • Avoid using wrist GPS. Although the latest models are much better in precision, antennas in those wrist compact models are less sensible that the ones in bigger models and so can be affected by GPS errors or loose satellite fixes.
  • Use different units. At least 3 units are recommended to average distances and have the chance to make error corrections.
  • Adjust to the same parameters on all GPS units. GPS systems have different parameters that can affect registered information. All units used in any measurement should be adjusted the same to valuate the information afterwards. This parameters can include:
    • Map Datum (WGS84)
    • Map units (Lat/Long, UTM)
    • Track registering frequency (Max distance 10m.)
    • Adjust the barometric data (according to the elevation of your start point)

Waypoint Registering

Along with tracks all measuring trip should register different waypoints along the route.

A waypoint is a precise location, with a unique Longitude and Latitude and can indicate anything that could be interesting to clarify the track: a river crossing, a rock a CP, etc.

It is very important to register in at least one of the GPS units all necessary waypoints. These waypoints will be fundamental on the postproduction phase to understand and locate elements along the route of the race.

Editing a track

Before having the proper measures it is important that we check the registered track. We should download it in a GPS program like BaseCamp (free from Garmin.com) and analyse the track looking for any possible errors, extra waypoints registered for any reason: out of route, lunch, take a look at something…

These track points should be cleaned and the track should have a single line of track points not farther than 10 m. from one to another. Any difference higher that that could mean that less distance was measured.

The final track can be saved as a GPX file and stored for further use, to be available for the runners to download or to obtain your race certification from ITRA.

It could also be interesting to have a track file with a maximum of 500 track points. This file could be downloadable because some old GPS units have a maximum of 500 points when importing a new track.

Anyway, you have to consider that with less track points the total distance will be less and the more track points that we have the more accurate the distance will be.