remove getConstant{Un}NormalizedProvider
The getConstant{Un}NormalizedProvider
methods in GravityFields
and GravityFieldFactory
are not well suited for modern gravity fields.
These models (like EIGEN-6S4v2) are piecewise, and may have discontinuities around
big earthquakes. The EIGEN-6S4v2 model for example has several discontinuities including
one around the 1985 Mexico earthquake, one around the 2004 Sumatra-Andaman earthquake,
one for the 2010 Chile earthquake and one for the 2011 Great Tohoku Earthquake.
Choosing a "constant" provider unambiguously is not possible. As part as solving issue #448 (closed),
we have implemented a freezing feature allowing to start from any provider, that may
be time-dependent, and to freeze it to some date. Then we have reimplemented getConstant{Un}NormalizedProvider
by freezing a provider to the latest reference date present in the filed (so for EIGEN-6S4v2,
we freeze it to a state after the 2011 Great Tohoku Earthquake.
The freezing feature seem to give users more control to the gravity field they use, so
getConstant{Un}NormalizedProvider
should probably be removed, and the freezing feature
moved up in the API. This will change user-facing interfaces.