As identified in #1091, Helmert implementation in PROJ 5.0 and 5.1 is confusing.
It happens that by default it used the coordinate_frame convention, contrary to
the position_vector convention used traditionaly for +towgs84. The documentation
of Helmert was also wrongly specifying that the default convention was
position_vector.
This commit:
- bans the confusing +transpose parameter
- removes the concept of a default convention, since in practice both are
equally found, and requires +convention as soon as a rotational term parameter
is present.
For translation only, convention is ignored and optional, as having no effect.
- fixes all the identified uses of proj=helmert in code, doc and tests
This is obviously a breaking change:
- users will have to adapt their pipeline expressions
- in particular, init files that would use helmert must be adapted
However, as designed, the break will be explicit, and not silent.