[PROJ] Some (probably dumb) questions about cs2cs and projinfo

[Greg Troxel]

Andrea Giudiceandrea via PROJ <proj at lists.osgeo.org> writes:

> Anyway, my concerns and doubts were firstly related to just
> understanding the reason why (although they all use the same PROJ and
> proj.db), cs2cs (and PostGIS and SpatiaLite) uses a particular
> (better) transformation, whereas QGIS another (worst) one, regardless
> of the fact that any of such transformations could be considered the
> right one.
>
> For that transformation, however, all the 5 available Helmert
> operations, the first one of which is used by cs2cs (and PostGIS and
> SpatiaLite), are much better than the ballpark operation used by QGIS
> (which can only choose between the grid shift operation and the
> ballpark one), since the ballpark is more than 100 metres off.

This seems like a good question to me.  I would (without any real
undertanding) expect qgis to offer the same set of pipelines with same
preference.

I've long had a concern that the EPSG database entries may not be
entirely right, and that when people talk about errors, etc., it's
always unclear if they mean the stated error in the EPSG entry, the best
believed error in the literature, or the actual error, compared to
something that is (validly!) believed to be better.  I really don't know
what's up here, but I suspect looking at it all carefully might turn up
some surprises.   If it doesn't, that's great, but it feels like news.