NHL: complete Simple Fault Surface

[Damiano Monelli]

The Simple Fault Surface is almost complete (see pull request: https://github.com/gem/NHE/pull/9).

A major revision is required only for the method get_strike().

The method get_strike() is supposed to return the fault strike as the average azimuth of the fault trace segments.

The average azimuth can be computed following the approach described in http://en.wikipedia.org/wiki/Mean_of_circular_quantities.

That is segment's azimuths and lengths are interpreted as polar coordinates and converted to cartesian coordinates (therefore defining a set of cartesian vectors). The mean azimuth is given by the angle of the vector obtained by summing all vectors.

A prototype of the method is available here: https://github.com/monellid/HazardEngine/blob/master/fault.py, method getStrike()

[Damiano Monelli (monelli)]

Test data for get_strike method