[PROJ] Vertical Transformations?

[Jeff McKenna]

I'm actually quite fine with the current way of managing grid files. 
But I believe everyone speaking here is the 1% of the 1% who understands 
this (I even include me ha), so when Andrew mentioned end-users, he is 
correct that 99.9% will not realize this requirement, and as packagers 
we can help the end-users and include all grid files.  (maybe this 
discussion is not for the PROJ list, but on a separate 'packagers' list, 
but, it comes up often in the sharing community) -jeff



On 2019-02-20 11:55 AM, Martin Desruisseaux wrote:
> 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
> 
>