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geodeticDatum: finding the correct EPSG codes #59

Open eclites opened 7 years ago

eclites commented 7 years ago

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 commented 7 years ago

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 commented 7 years ago

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 commented 7 years ago

Hi @eclites Note (and @tucotuco will weigh in here) that if you search for "NAD27" here: https://epsg.io/ you get a list, image 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 commented 7 years ago

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 commented 7 years ago

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

dagendresen commented 7 years ago

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)