[PROJ] Vertical Transformations?

[Martin Desruisseaux]

Le 20/02/2019 à 16:09, Jeff McKenna a écrit :

> Most do not know what a grid is, and will unfortunately (as of now)
> use the incorrect coordinates and later face grief trying to
> understand why their data doesn't match in their application
>
Even if all grids were supplied, transformations would still have a
limited accuracy. Users should look at the accuracy information in order
to judge if the transformation is okay for their needs (this implies
that QGIS, PostGIS, etc. should make this information easily available).
Users do not need to know the details of datum shift operations (i.e.
whether a grid is used of not), but the accuracy information is
mandatory for anyone doing scientific or engineering work. One could
object that not every users are scientist or engineer, but if a user
does not care about accuracy then he should not have grief if the data
appear shifted.

I think we should not push too far the desire to provide a black box. I
agree about hiding implementation details, but not about hiding the fact
that every transformations have a limited accuracy - this problem has
its root in the physical world and is above any map projection library.
Luring the users with the false impression that coordinate operations
have an infinite accuracy is one cause of problems we have with
inter-operability between software using different referencing libraries.

    Martin