[PROJ] "Local" projection method?

[Nyall Dawson]

Hi list,

I've just come across a WKT CRS definition which looks like this:

PROJCS[".....",
  GEOGCS["GCS_WGS_1984",
    DATUM["D_WGS_1984",
      SPHEROID["WGS_1984",6378137.0,298.257223563]
    ],
    PRIMEM["Greenwich",0.0],
    UNIT["Degree",0.0174532925199433]],
  PROJECTION["Local"],
  PARAMETER["False_Easting",#####.##],
  PARAMETER["False_Northing",#####.###],
  PARAMETER["Scale_Factor",1.0],
  PARAMETER["Azimuth",0.0],
  PARAMETER["Longitude_Of_Center",###.####],
  PARAMETER["Latitude_Of_Center",##.####],
  UNIT["Meter",1.0]
]

(actual values replaced by # for confidentiality).

Currently proj converts this to:

PROJCRS["...",
    BASEGEOGCRS["WGS 84",
        DATUM["World Geodetic System 1984",
            ELLIPSOID["WGS 84",6378137,298.257223563,
                LENGTHUNIT["metre",1]],
            ID["EPSG",6326]],
        PRIMEM["Greenwich",0,
            ANGLEUNIT["Degree",0.0174532925199433]]],
    CONVERSION["unnamed",
        METHOD["Local"],
         ...

Which then fails to convert any coordinates, due to the unknown "Local" method.

I've been trying to research exactly what this "Local" projection means.

There's some documentation for it here:
https://pro.arcgis.com/en/pro-app/help/mapping/properties/local.htm

Which states:

"The local projection is a specialized map projection that does not
take into account the curvature of the earth. The coordinates of the
center of the area of interest define the origin of the local
coordinate system. The plane is tangent to the spheroid at that point,
and the differences in z-values are negligible between corresponding
points on the spheroid and the plane. This map projection is the same
as the orthographic projection but supported on ellipsoids and
spheres, while the orthographic projection is supported on spheres
only."

Based on this, would it be appropriate to directly map this projection
method across to the "Orthographic" method? Or am I missing something
important?...

Nyall