geodeticDatum: finding the correct EPSG codes

[eclites]

I am having trouble using https://www.epsg-registry.org/ to find the correct EPSG code for my data. From the current aggregator summaries, ESPG::4326 seems to be WGS84. I'm not sure about NAD83 or NAD27. The search results I got when searching the registry don't match codes anyone is currently serving, which probably means I've made an error.

[tucotuco]

You got WGS84 correct (see https://epsg.io/4326). Here is a great page of information on NAD27 (https://epsg.io/4267) and here is one for NAD83 (https://epsg.io/4269).

[eclites]

Thanks! Are there any better ways to do searches on those webpages to find the codes? I got so many results, it was intimidating to look through.

[debpaul]

Hi @eclites Note (and @tucotuco will weigh in here) that if you search for "NAD27" here: https://epsg.io/ you get a list,

Note that from all in the list John has pointed you to the most general one (the same way I pointed you to the WGS84 https://epsg.io/4326 equivalent some weeks ago), namely https://epsg.io/4267 for NAD27. The others are specific instances of NAD27 - and I believe the only reason you'd map to those was if you knew for certain, from your specimen documentation, that one of these was specified. When in doubt, post a question to us here, or perhaps the iDigBio GWG for answers.

[debpaul]

I am proposing to add this documentation to the https://github.com/tdwg/dwc-qa/wiki/Georeferences resource. @tucotuco how do we answer @eclites conundrum about "got so many results, it was intimidating to look through." Is there a search strategy we can offer? Is there a "usual suspects" list we can offer (like a table for this EPSG code = this geodeticDatum)? Perhaps we use (reference) this one:
EPSG:4326: WGS84
EPSG:4269: NAD83
EPSG:4267: NAD27
found here https://terms.tdwg.org/wiki/dwc:geodeticDatum
Note @pzermoglio this also is something we could reference here: https://github.com/tdwg/dwc-qa/wiki/Controlled-Vocabularies

[debpaul]

Note that I started the https://github.com/tdwg/dwc-qa/wiki/Georeferences#geodeticDatum section

[dagendresen]

Notice that the EPSG code refers to both the datum AND the projection. E.g. I believe that EPSG code 4269 is NAD83 unprojected (coordinates presented as decimaldegrees). You will find very many other EPSG codes for NAD83 with other projections.

http://epsg.io/4269
http://epsg.io/?q=NAD83
http://spatialreference.org/ref/epsg/4269/
http://spatialreference.org/ref/?page=14&search=NAD83

Suggest update such a list to:
EPSG:4326: WGS84 unprojected
EPSG:4269: NAD83 unprojected
EPSG:4267: NAD27 unprojected

EPSG:3373 = NAD83 UTM 60N
EPSG:3371 = NAD27 UTM 60N

(PS: I simply have a list with EPSG codes I often use on a sticker on the wall next to my desk)