[PROJ] Vertical Transformations?

[Greg Troxel]

Even Rouault <even.rouault at spatialys.com> writes:

> We could enhance the PROJ database with a table/column to flag required 
> transformation, but it is probably not trivial (area of use comes into the 
> equation), and that would put the PROJ project in a position of being an 
> "authority" to decide which transformation are required or not.

That sounds like a good path.

I don't see the authority problem; when implementing a transformation
that is defined to use a grid file, it's pretty clear that it can't be
done the same way without it.

If you mean the issue of a coarser transformation with assumed zero
shift, it seems that introducing that transformation as avlid is what's
problematic.

My real issue is people not getting the answer that is expected because
of not spending time on grid files that they might not even know exist.

Thanks for the discussion; we are either at (or beyond :-) the point
where further comments from me are helpful, and as always I learned
something.


Earlier I said that I included the grid files with proj, and I meant the
base proj-datumgrids, which I had thought were viewed as optional.  I
see now that they are declared as required, and that there are new
regional datumngrid files that have arisen in the last year (which have
the NGVD29 stuff).  I'm in the process of updating the pkgsrc package to
have the new regional files also.