[PROJ] Datum Grids, Which Ones?

[Paul Ramsey]

So, just as a confirmation: being a stupid ape and just blindly installing every datumgrid.zip file I can get my hand on will lead to the “best” results? 

> On Sep 30, 2019, at 1:28 PM, Kristian Evers <kristianevers at gmail.com> wrote:
> 
> Yes, this could do with some clarification in the docs. Briefly, it goes something like this:
> 
> proj-datumgrid is the original datumgrid packages. It contains mostly basic North American grids,
> a few European grids and the egm96 geoid model. The test suite will fail without this. Many
> transformations will work without it. These days this package is mostly kept for legacy reasons.
> 
> The regional grid packages contain grids and other resources that are useful in those regions.
> Currently three regions are covered. The grids are split in these packages to avoid consuming
> too much disk space for users who has that concern. If you have plenty of space just get all of them.
> 
> The world package is for grids that has global coverage. Currently only the egm08_25.gtx grid is
> in that package. It is NOT a package containing all grids of the world.
> 
> 
> We have previously talked about adding a -all package which holds everything. This will be easier
> for most people to use it seems. I haven’t gotten around to it because it requires changing the
> CMake setup of the proj-datumgrids repository [0] and that is just not a job that I am particularly keen
> on doing. A pull requests adding this is welcome.
> 
> Finally, Howard is trying to find the funds to deal with grids in a smarter way. I suggest that those
> who can support his effort.
> 
> /Kristian
> 
> [0] https://github.com/OSGeo/proj-datumgrid
> 
> 
>> On 30 Sep 2019, at 22:09, Paul Ramsey <pramsey at cleverelephant.ca> wrote:
>> 
>> The list of datum grids on the web side is not 100% clear on what grids a person should pull for what purpose…
>> There’s regional files (europe and na and oceania) there’s a “world” file which, by size, perhaps includes all of the above? and there’s the un-specialized file, proj-datumgrid that is… everything not in the other files? something else?
>> 
>> 
>> • 2018-09-15 proj-datumgrid-1.8.zip
>> 
>> • 2019-09-01 proj-datumgrid-europe-1.4.zip
>> 
>> • 2019-03-01 proj-datumgrid-north-america-1.2.zip
>> 
>> • 2018-03-01 proj-datumgrid-oceania-1.0.zip
>> 
>> • 2019-03-01 proj-datumgrid-world-1.0.zip
>> 
>> If the best practice is just “download’em’all if you have the space”, then an “all” might be good, instead of “world”. And some note on what proj-datumgrid-1.8.zip actually is? Is it for Proj < 6 only?
>> 
>> P
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