EPSG:7891

COORDINATEOPERATION["SHGD2015 to SHVD2015 height (1)",
    VERSION["ENRD-Shn Hel"],
    SOURCECRS[
        GEOGCRS["SHGD2015",
            DATUM["St. Helena Geodetic Datum 2015",
                ELLIPSOID["GRS 1980",6378137,298.257222101,
                    LENGTHUNIT["metre",1]]],
            PRIMEM["Greenwich",0,
                ANGLEUNIT["degree",0.0174532925199433]],
            CS[ellipsoidal,3],
                AXIS["geodetic latitude (Lat)",north,
                    ORDER[1],
                    ANGLEUNIT["degree",0.0174532925199433]],
                AXIS["geodetic longitude (Lon)",east,
                    ORDER[2],
                    ANGLEUNIT["degree",0.0174532925199433]],
                AXIS["ellipsoidal height (h)",up,
                    ORDER[3],
                    LENGTHUNIT["metre",1]],
            ID["EPSG",7885]]],
    TARGETCRS[
        VERTCRS["SHVD2015 height",
            VDATUM["St. Helena Vertical Datum 2015"],
            CS[vertical,1],
                AXIS["gravity-related height (H)",up,
                    LENGTHUNIT["metre",1]],
            ID["EPSG",7890]]],
    METHOD["Geographic3D to GravityRelatedHeight (EGM2008)",
        ID["EPSG",1025]],
    PARAMETERFILE["Geoid (height correction) model file","Und_min2.5x2.5_egm2008_isw=82_WGS84_TideFree.gz"],
    OPERATIONACCURACY[0.0],
    USAGE[
        SCOPE["Derivation of gravity-related heights from GNSS observations."],
        AREA["St Helena, Ascension and Tristan da Cunha - St Helena Island - onshore."],
        BBOX[-16.08,-5.85,-15.85,-5.59]],
    ID["EPSG",7891],
    REMARK["This transformation defines SHVD2015 heights. For reversible alternative to this transformation see SHGD2015 to SHGD2015 + SHVD2015 height (1) (code 9617)."]]

proj4.defs("EPSG:7891","+proj=pipeline +step +proj=axisswap +order=2,1 +step +proj=unitconvert +xy_in=deg +xy_out=rad +step +inv +proj=vgridshift +grids=us_nga_egm08_25.tif +multiplier=1 +step +proj=unitconvert +xy_in=rad +xy_out=deg +step +proj=axisswap +order=2,1");

{
    "$schema": "https://proj.org/schemas/v0.7/projjson.schema.json",
    "type": "Transformation",
    "name": "SHGD2015 to SHVD2015 height (1)",
    "source_crs": {
        "type": "GeographicCRS",
        "name": "SHGD2015",
        "datum": {
            "type": "GeodeticReferenceFrame",
            "name": "St. Helena Geodetic Datum 2015",
            "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"
                },
                {
                    "name": "Ellipsoidal height",
                    "abbreviation": "h",
                    "direction": "up",
                    "unit": "metre"
                }
            ]
        },
        "id": {
            "authority": "EPSG",
            "code": 7885
        }
    },
    "target_crs": {
        "type": "VerticalCRS",
        "name": "SHVD2015 height",
        "datum": {
            "type": "VerticalReferenceFrame",
            "name": "St. Helena Vertical Datum 2015"
        },
        "coordinate_system": {
            "subtype": "vertical",
            "axis": [
                {
                    "name": "Gravity-related height",
                    "abbreviation": "H",
                    "direction": "up",
                    "unit": "metre"
                }
            ]
        },
        "id": {
            "authority": "EPSG",
            "code": 7890
        }
    },
    "method": {
        "name": "Geographic3D to GravityRelatedHeight (EGM2008)",
        "id": {
            "authority": "EPSG",
            "code": 1025
        }
    },
    "parameters": [
        {
            "name": "Geoid (height correction) model file",
            "value": "Und_min2.5x2.5_egm2008_isw=82_WGS84_TideFree.gz",
            "id": {
                "authority": "EPSG",
                "code": 8666
            }
        }
    ],
    "accuracy": "0.0",
    "scope": "Derivation of gravity-related heights from GNSS observations.",
    "area": "St Helena, Ascension and Tristan da Cunha - St Helena Island - onshore.",
    "bbox": {
        "south_latitude": -16.08,
        "west_longitude": -5.85,
        "north_latitude": -15.85,
        "east_longitude": -5.59
    },
    "id": {
        "authority": "EPSG",
        "code": 7891
    },
    "remarks": "This transformation defines SHVD2015 heights. For reversible alternative to this transformation see SHGD2015 to SHGD2015 + SHVD2015 height (1) (code 9617)."
}

<?xml version="1.0" encoding="utf-8"?>
<Map srs="+proj=pipeline +step +proj=axisswap +order=2,1 +step +proj=unitconvert +xy_in=deg +xy_out=rad +step +inv +proj=vgridshift +grids=us_nga_egm08_25.tif +multiplier=1 +step +proj=unitconvert +xy_in=rad +xy_out=deg +step +proj=axisswap +order=2,1">
	<Layer srs="+proj=pipeline +step +proj=axisswap +order=2,1 +step +proj=unitconvert +xy_in=deg +xy_out=rad +step +inv +proj=vgridshift +grids=us_nga_egm08_25.tif +multiplier=1 +step +proj=unitconvert +xy_in=rad +xy_out=deg +step +proj=axisswap +order=2,1">
	</Layer>
</Map>

INSERT into spatial_ref_sys (srid, auth_name, auth_srid, proj4text, srtext) values ( 7891, 'EPSG', 7891, '+proj=pipeline +step +proj=axisswap +order=2,1 +step +proj=unitconvert +xy_in=deg +xy_out=rad +step +inv +proj=vgridshift +grids=us_nga_egm08_25.tif +multiplier=1 +step +proj=unitconvert +xy_in=rad +xy_out=deg +step +proj=axisswap +order=2,1', 'None');