[PROJ] On Looking Up ESRI WKIDs

[Nyall Dawson]

On Wed, 27 Apr 2022 at 08:21, Peter Townsend via PROJ
<proj at lists.osgeo.org> wrote:
>
> Greetings! I'm going to be responding to calls to a FeatureServer and it gives me back a response that looks like this:
>
>
> 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.

It's certainly NOT an authoritative answer, but QGIS' logic looks like this:

- If "latestWkid" value present, use that. Otherwise use "wkid"
- Try creating a crs from "EPSG:" + wkid. If that doesn't exist, try
"ESRI:" + wkid
- If neither "latestWkid" nor "wkid" is present, build the crs from
the "wkt" value
- If everything else fails, use EPSG:3857, since most ESRI services
default to this.

I'm eagerly watching this thread for more definitive answers though!

Nyall


>
> --
> Peter Townsend
> Senior Software Developer
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