EPSG:9312

COORDINATEOPERATION["NZVD2016 height to Auckland 1946 height (2)",
    VERSION["LINZ-NZ AUCK gtx"],
    SOURCECRS[
        VERTCRS["NZVD2016 height",
            VDATUM["New Zealand Vertical Datum 2016"],
            CS[vertical,1],
                AXIS["gravity-related height (H)",up,
                    LENGTHUNIT["metre",1]],
            ID["EPSG",7839]]],
    TARGETCRS[
        VERTCRS["Auckland 1946 height",
            VDATUM["Auckland 1946"],
            CS[vertical,1],
                AXIS["gravity-related height (H)",up,
                    LENGTHUNIT["metre",1]],
            ID["EPSG",5759]]],
    METHOD["Vertical Offset by Grid Interpolation (gtx)",
        ID["EPSG",1084]],
    PARAMETERFILE["Vertical offset file","auckht1946-nzvd2016.gtx"],
    INTERPOLATIONCRS[
        GEOGCRS["NZGD2000",
            DATUM["New Zealand Geodetic Datum 2000",
                ELLIPSOID["GRS 1980",6378137,298.257222101,
                    LENGTHUNIT["metre",1]]],
            PRIMEM["Greenwich",0,
                ANGLEUNIT["degree",0.0174532925199433]],
            CS[ellipsoidal,2],
                AXIS["geodetic latitude (Lat)",north,
                    ORDER[1],
                    ANGLEUNIT["degree",0.0174532925199433]],
                AXIS["geodetic longitude (Lon)",east,
                    ORDER[2],
                    ANGLEUNIT["degree",0.0174532925199433]]]],
    OPERATIONACCURACY[0.02],
    USAGE[
        SCOPE["Change of height to a different vertical reference surface."],
        AREA["New Zealand - North Island - Auckland vertical CRS area."],
        BBOX[-37.67,174,-36.12,176.17]],
    ID["EPSG",9312],
    REMARK["Derived at 260 control points. Mean offset 0.292m, standard deviation 0.029m, maximum difference from mean 0.075m. Supersedes NZVD2016 height to Auckland 1946 height (1) (code 7860) after change of grid file format."]]

proj4.defs("EPSG:9312","+proj=vgridshift +grids=nz_linz_auckht1946-nzvd2016.tif +multiplier=1");

{
    "$schema": "https://proj.org/schemas/v0.7/projjson.schema.json",
    "type": "Transformation",
    "name": "NZVD2016 height to Auckland 1946 height (2)",
    "source_crs": {
        "type": "VerticalCRS",
        "name": "NZVD2016 height",
        "datum": {
            "type": "VerticalReferenceFrame",
            "name": "New Zealand Vertical Datum 2016"
        },
        "coordinate_system": {
            "subtype": "vertical",
            "axis": [
                {
                    "name": "Gravity-related height",
                    "abbreviation": "H",
                    "direction": "up",
                    "unit": "metre"
                }
            ]
        },
        "id": {
            "authority": "EPSG",
            "code": 7839
        }
    },
    "target_crs": {
        "type": "VerticalCRS",
        "name": "Auckland 1946 height",
        "datum": {
            "type": "VerticalReferenceFrame",
            "name": "Auckland 1946"
        },
        "coordinate_system": {
            "subtype": "vertical",
            "axis": [
                {
                    "name": "Gravity-related height",
                    "abbreviation": "H",
                    "direction": "up",
                    "unit": "metre"
                }
            ]
        },
        "id": {
            "authority": "EPSG",
            "code": 5759
        }
    },
    "interpolation_crs": {
        "type": "GeographicCRS",
        "name": "NZGD2000",
        "datum": {
            "type": "GeodeticReferenceFrame",
            "name": "New Zealand Geodetic Datum 2000",
            "ellipsoid": {
                "name": "GRS 1980",
                "semi_major_axis": 6378137,
                "inverse_flattening": 298.257222101
            }
        },
        "coordinate_system": {
            "subtype": "ellipsoidal",
            "axis": [
                {
                    "name": "Geodetic latitude",
                    "abbreviation": "Lat",
                    "direction": "north",
                    "unit": "degree"
                },
                {
                    "name": "Geodetic longitude",
                    "abbreviation": "Lon",
                    "direction": "east",
                    "unit": "degree"
                }
            ]
        },
        "id": {
            "authority": "EPSG",
            "code": 4167
        }
    },
    "method": {
        "name": "Vertical Offset by Grid Interpolation (gtx)",
        "id": {
            "authority": "EPSG",
            "code": 1084
        }
    },
    "parameters": [
        {
            "name": "Vertical offset file",
            "value": "auckht1946-nzvd2016.gtx",
            "id": {
                "authority": "EPSG",
                "code": 8732
            }
        }
    ],
    "accuracy": "0.02",
    "scope": "Change of height to a different vertical reference surface.",
    "area": "New Zealand - North Island - Auckland vertical CRS area.",
    "bbox": {
        "south_latitude": -37.67,
        "west_longitude": 174,
        "north_latitude": -36.12,
        "east_longitude": 176.17
    },
    "id": {
        "authority": "EPSG",
        "code": 9312
    },
    "remarks": "Derived at 260 control points. Mean offset 0.292m, standard deviation 0.029m, maximum difference from mean 0.075m. Supersedes NZVD2016 height to Auckland 1946 height (1) (code 7860) after change of grid file format."
}

<?xml version="1.0" encoding="utf-8"?>
<Map srs="+proj=vgridshift +grids=nz_linz_auckht1946-nzvd2016.tif +multiplier=1">
	<Layer srs="+proj=vgridshift +grids=nz_linz_auckht1946-nzvd2016.tif +multiplier=1">
	</Layer>
</Map>

INSERT into spatial_ref_sys (srid, auth_name, auth_srid, proj4text, srtext) values ( 9312, 'EPSG', 9312, '+proj=vgridshift +grids=nz_linz_auckht1946-nzvd2016.tif +multiplier=1', 'None');