Altitude calculation in tracks

Tracks contain altitude information at their points, which allows displaying altitude graphs and calculating properties such as total ascent, maximum altitude, or elevation changes.

The accuracy of this data depends on the source of the altitude information. Tracks recorded on GPS devices with a barometric altimeter usually have accurate altitudes, but other devices without a barometric altimeter tend to be less precise. 

Tracks created over a map can also include altitude data, calculated based on elevation models (DEM), also known as reliefs. The accuracy of these reliefs can vary.

Reliefs available in Land

Land provides users with different relief models, some of them free and others available for download:

• World_Base_Relief (online, free)
  • Available by default. ( Data Tree > Online Maps > World > World_Base Relief.cwdem)
  • No download required: it loads automatically in small cells as needed.

  • Resolution of 90 x 90 m, sufficient for general reference.

    

• Downloadable reliefs  3D Reliefs (depending on country or level of detail):
  • Standard: 90 x 90 m
  • HD: 30 x 30 m
  • UltraHD (e.g. France): 5 x 5 m

The higher the resolution of the relief, the more accurate the altitude data associated with tracks created on it will be.

Recalculate altitudes in Land

• Right-click on the open track > Tools > Calculate land altitude for each point

If a track has incorrect or missing altitude data, Land allows you to recalculate it.

The calculation is based on the relief currently loaded.

Ascent calculation settings

The values for total ascent and descent are calculated using an algorithm that filters out small altitude changes (noise or inaccuracies) caused by imprecise data.

This filtering is controlled by the "Minimum altitude change to accumulate" parameter.

• File > Preferences > Tracks > Min.Altitude. ncrease

This parameter defines the minimum altitude change required for it to be counted as part of the ascent.

If the ascent values shown in your track are too high, it’s likely that small variations in altitude (due to relief or GPS inaccuracy) are being counted.
In that case, it’s advisable to increase the “Minimum altitude change to accumulate” so the calculation ignores minor changes and only sums significant elevation gains.

On the other hand, if ascent values seem too low, it may be that the system is ignoring relevant changes in altitude. In this case, you can reduce the value of “Minimum altitude change to accumulate” so more variations are considered and the calculation is more complete.

This setting is also available on TwoNav devices. It is important to configure the same value for “Minimum altitude change to accumulate” in both TwoNav and Land, to ensure consistent ascent data for the same track.