How is the altitude profile (altitude data) of the rides determined?

When recording the journey via smartphone, only the lat/lon data of the route are recorded and used for the calculation of the ACTYVOLTS...

When recording the journey via smartphone, only the lat/lon data of the route are recorded and used for the calculation of the ACTYVOLTS by means of an algorithm. The elevation data is added outside the app. An altitude database (by ACTYVO) is used which adds all altitude profiles available worldwide to the lat/lon data and calculates the altitude profile of the rides.
This approach is used so that the altitude data recorded on different devices are taken into account uniformly and fairly in the calculation of the results (ACTYVOLTS).