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docs/features/costfunctions.md

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+## Freely configurable routing profile
+
+A major reason for the limited usefulness of most bike routing software is that
+routing preferences are a personal issue. Not even will MTB and racing cyclist
+never agree on common routing preferences, also the same people will have
+different preferences for day and night, dry and wet weather, etc. The only
+solution for that problem is the use of a freely configurable cost function that
+can easily be adapted to personal needs. This is far more flexible compared to a
+set of static functions with a fixed set of configuration variables.
+
+To make that point somewhat clearer: there are other routers that are highly
+configurable, look at [routino](http://www.routino.org/uk/router.html) for an
+example. However, these are one-dimensional parameter sets that do not allow to
+handle arbitrary correlation. BRouter's configuration is different. It is more a
+scripting language that allows you to program the cost function instead of just
+configuring it. E.g. a non-graded track is generally not a good track. But if it
+has a surface=asphalt tag, it probably is. On the other hand, a grade5-track
+with surface=asphalt is primarily a grade5-track and you should not ignore that.
+Such logic is not implementable in one-dimensional parameter sets.
+
+See some [sample profiles](profiles2) provided for the online router.
+
+See the trekking-profile [`trekking.brf`](profiles2/trekking.brf) as the
+reference-profile with some explanations on the meaning of this script.
+
+See the [profile_developers_guide.txt](profile_developers_guide.txt) for a
+technical reference.