[PROJ] Getting "proj" and "datum" for a CRS

[Kristian Evers]

> On 7 May 2019, at 11:37, Even Rouault <even.rouault at spatialys.com> wrote:
> 
>>> I'd note that adding a new member to PJ_PROJ_INFO will change the ABI in a
>>> incompatible manner. Will/would require a libtool 'current' bump
>> 
>> So is this a -1 on this change? I'm conscious the deadline is closing
>> for 6.1....
> 
> I'm indifferent. Was mostly to bring that to the attention of Kristian.
> 

Thanks :-) I am of the opinion that we should avoid incompatible changes for
this release. When suggested adding more to PJ_PROJ_INFO I didn’t realize
that it would affect the ABI.

In addition, after having giving this some more though I think there must be a
better way to deal with this problem. A generic function that can returns all
parameters that make up a PJ object would be preferable. A wrapper for
pj_param() would do the trick but a better way likely exists. 


>> 
>> At the moment I'm wondering if I'll need to just resort to a regex to
>> get this property (argh!) 
> 
> In an ideal world, QGIS should avoid messing directly with PROJ strings (I 
> guess this is for some backward compatibility reason regarding QGIS API). 
> Especially regarding extracting elements from them. Treating the whole string 
> as an opaque string might be acceptable, although not the most precise 
> representation compared to using WKT or directly the EPSG:XXXX representation 
> when available (I know I repeat myself on this, but this is for the education 
> of the crowds :-))
> 
> Even
> 
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