[GRASS-dev] Location wizard (missed window to select +towgs params)

[Hamish]

Markus wrote:
> FrankW has published a blog with details:
> 
> http://fwarmerdam.blogspot.com/2010/03/in-last-few-weeks-i-believe-i-have-made.html
> 
> Perhaps that's giving more insights.

it does:

[...]
"While this got rid of one family of errors, it also triggered lots of additional frustration and confusion. Part of this was just because there was a change of behavior. But it was also pushing people a bit harder to determine the appropriate datum shift and they did not like having to do this.

So, at last, I have taken the plunge and reworked the scripts used to translate the EPSG dictionary so that they attempt to pick one shift if there are several available. I follow a few heuristics in this effort."
[...]


In the past GRASS has sided with correctness over convinence
(aka save time in the long term vs. short term); I suggest we
figure out a way to stick with our old "show the user a list 
of alternatives and make them choose (forcing them to look it
up or make some phone calls, if necessary)" method.
it may be a PITA but in the long term you are doing them a big
favour. Software which are primarily data-viewers may have other
priorities of course.


"Currently GDAL, and the PROJ.4 dictionary are just using the preferred datum shift. But the intention of keeping the datum_shift.csv file with all the possible shifts for any given GCS is that savvy applications could let the user choose."


so for future merging we'll have to be more savvy.
(I'm pretty happy with our internal dautm.table and
datumtransform.table to be honest)

until then, I guess we revert the .csv files, while checking
for intermingled bug fixes if possible.


"datum_shift_pref.csv" prefers the 7-term NZGD49 transform over
the 3-term. But that ignores the NTv2 file if present(??).
And often you are given data known to be in the "less desirable"
transform parms (still used by the vast majority of other
software) but documented numeric consistency is more important
that keeping up with the latest transform ideas.


make 'em eat their veggies,
Hamish