[PROJ] On Looking Up ESRI WKIDs

[Peter Townsend]

Greetings! I'm going to be responding to calls to a FeatureServer and it
gives me back a response that looks like this:

{
  "objectIdFieldName": "objectid",
  "globalIdFieldName": "",
  "geometryType": "esriGeometryPoint",
  "spatialReference": {
    "wkid": 26949,
    "latestWkid": 26949
  },
  "fields": [
    {
      "name": "objectid",
      "alias": "OBJECTID",
      "type": "esriFieldTypeOID"
    },
    ...
  ],
  "features": [
    {
      "attributes": {
        "objectid": 1,
        "cities_lam": 25552,
        "cities_l_1": 25552,
        "citiesx020": 25552,
        "feature": "Populated Place",
        "name": "Harris",
        "pop_range_": "Undetermined",
        "pop_90": -99999,
        "pop_98": -99999,
        "fips55": "31320",
        "county": "Mohave County",
        "fips": "04015",
        "state": "AZ",
        "state_fips": "04",
        "display": 0
      },
      "geometry": {
        "x": 15704.363599999808,
        "y": 460919.1546
      }
    },
    ...
  ]
}

It's obviously ESRI related. The problem is the "wkid"/"latestWkid" field.
We'd like to turn that into a PROJ CRS lookup. In the case of 26949, it
turns out to match up nicely to EPSG:26949, aka "NAD83 / Arizona Central".
In the ARCGIS docs, it has the name
"NAD_1983_StatePlane_Arizona_Central_FIPS_0202". A PROJ CRS lookup by that
name also returns EPSG:26949.

But then consider WKID 102649. It's outside of the EPSG code range, right?
So EPSG:102649 doesn't turn up anything. But it is findable under
ESRI:102649, with the name
"NAD_1983_StatePlane_Arizona_Central_FIPS_0202_Feet".

My question is thus, is it safe to assume that if I encounter an ESRI wkid
greater than 32767 that I should try looking it up with the ESRI authority?
And less than or equal, that it is the same as the EPSG code?

A quick search through the list history found me a semi-related question
from 11 years ago that kind of implies this, so it wouldn't hurt to ask
again.

-- 
Peter Townsend
Senior Software Developer
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