[PROJ] Questions about declaring a CRS

[Martin Desruisseaux]

Hello Floris

If a choice is possible, I would encourage to use one of the approaches 
recognized by international standards:

  * Authority codes with axis order and units as defined by authority
    (e.g. "EPSG:4326" is /latitude/, /longitude/; if the reverse order
    is wanted then "CRS:84" can be used instead).
  * Well Known Text version 2 (a.k.a. ISO 19162).
  * Possibly the JSON format cited by Even in the future.

PROJ 6 and later support all the above. I think they are preferable to 
PROJ strings for at least 2 reasons:

  * They are portable, with WKT 2 possibly the safest bet for now since
    it is an existing OGC and ISO standard. While PROJ is the most
    popular, it is nevertheless not the only map projection engine
    available, with each engine having their advantage and inconvenient.
    Other map projection engines are more likely to understand a CRS
    defined by international standards than by PROJ-specific strings.
    Even if R uses only PROJ, a R script may want to fetch data from a
    distant server backed by a different map projection engine.
  * For educational reason: the PROJ string syntax evolved from a system
    initially designed for map projections only, not for the more
    general context of transformations between arbitrary pairs of CRS.
    If users educate themselves by learning from PROJ strings, there is
    a risk that they confuse CRS with operations, that they believe that
    "+towgs84" is good practice, etc.

Regards,

     Martin


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