Add an option to export only the mean curves

[Michele Simionato]

This was requested by an user: https://groups.google.com/forum/#!topic/openquake-users/GYHWuba2x98

[Michele Simionato (michele-simionato)]

This is especially important when there are several realizations and probably it should be default in that case.

[Michele Simionato (michele-simionato)]

Some clarification is needed for the event based case. For instance, a meaningful use case is to compare the mean hazard curves produced by the event based calculator with sampling with the mean hazard curves produced by the classical calculator with full enumeration. In order to implement such use case efficiently, the engine must be able to produce the mean curves without storing in the database both the individual curves and the ground motion fields. That's not the problem. The question is: should we support other use cases? In particular, should the engine be able to compute mean ground motion fields or not?

[Michele Simionato (michele-simionato)]

Damiano says no.

[Michele Simionato (michele-simionato)]

https://github.com/gem/oq-engine/pull/1516