L - Algorithms
A fast algorithm is giving the distance similarity (DistSim) based on the latitude and longitude with a precision of 0.5 %.
The value is 1.0 if both points are identical, and 0.0 if they are exactly on opposite faces of the earth, thus separated by approx. 20000 km.
The altitude similarity (AltSim) is computed so that the result is 1.0 for points at the same altitude and 0.0 if the altitude difference is 8000 meters.
Five algorithms are available:
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Distance only: the returned value is DistSim.
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Distance mainly: The result is 0.75 * DistSim + 0.25 * AltSim
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Altitude only: the result is AltSim
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Altitude mainly: the result is 0.75 * AltSim + 0.25 * DistSim
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Both: the result is 0.5 * DistSim + 0.5 * AltSim
The precision factor is also used in the computation of the similarity.
For example, two points distant from each other of 500 km, the first one having a PF of 12 km and the second one of 5 km, the computed distance between the two will be 500-12-5 = 483 km.
This will then be transformed into a similarity coefficient.