EPSG:7971

COORDINATEOPERATION["NGVD29 height (m) to NAVD88 height (3)",
    VERSION["NGS-US Conus E"],
    SOURCECRS[
        VERTCRS["NGVD29 height (m)",
            VDATUM["National Geodetic Vertical Datum 1929"],
            CS[vertical,1],
                AXIS["gravity-related height (H)",up,
                    LENGTHUNIT["metre",1]],
            ID["EPSG",7968]]],
    TARGETCRS[
        VERTCRS["NAVD88 height",
            VDATUM["North American Vertical Datum 1988"],
            CS[vertical,1],
                AXIS["gravity-related height (H)",up,
                    LENGTHUNIT["metre",1]],
            ID["EPSG",5703]]],
    METHOD["Vertical Offset by Grid Interpolation (VERTCON)",
        ID["EPSG",9658]],
    PARAMETERFILE["Vertical offset file","vertcone.94"],
    OPERATIONACCURACY[0.02],
    USAGE[
        SCOPE["Change of height to a different vertical reference surface."],
        AREA["United States (USA) - CONUS east of 89°W - onshore - Alabama; Connecticut; Delaware; Florida; Georgia; llinois; Indiana; Kentucky; Maine; Maryland; Massachusetts; Michigan; Mississippi; New Hampshire; New Jersey; New York; North Carolina; Ohio; Pennsylvania; Rhode Island; South Carolina; Tennessee; Vermont; Virginia; West Virginia; Wisconsin."],
        BBOX[24.41,-89,48.32,-66.91]],
    ID["EPSG",7971],
    REMARK["In this area the NGVD29 vertical reference surface is approximately 0 to 0.5m above the NAVD88 surface. Interpolation within the gridded data file may be made using either NAD27 or any of the realisations of NAD83 applicable to US conus."]]

proj4.defs("EPSG:7971","+proj=vgridshift +grids=us_noaa_vertcone.tif +multiplier=1");

{
    "$schema": "https://proj.org/schemas/v0.7/projjson.schema.json",
    "type": "Transformation",
    "name": "NGVD29 height (m) to NAVD88 height (3)",
    "source_crs": {
        "type": "VerticalCRS",
        "name": "NGVD29 height (m)",
        "datum": {
            "type": "VerticalReferenceFrame",
            "name": "National Geodetic Vertical Datum 1929"
        },
        "coordinate_system": {
            "subtype": "vertical",
            "axis": [
                {
                    "name": "Gravity-related height",
                    "abbreviation": "H",
                    "direction": "up",
                    "unit": "metre"
                }
            ]
        },
        "id": {
            "authority": "EPSG",
            "code": 7968
        }
    },
    "target_crs": {
        "type": "VerticalCRS",
        "name": "NAVD88 height",
        "datum": {
            "type": "VerticalReferenceFrame",
            "name": "North American Vertical Datum 1988"
        },
        "coordinate_system": {
            "subtype": "vertical",
            "axis": [
                {
                    "name": "Gravity-related height",
                    "abbreviation": "H",
                    "direction": "up",
                    "unit": "metre"
                }
            ]
        },
        "id": {
            "authority": "EPSG",
            "code": 5703
        }
    },
    "method": {
        "name": "Vertical Offset by Grid Interpolation (VERTCON)",
        "id": {
            "authority": "EPSG",
            "code": 9658
        }
    },
    "parameters": [
        {
            "name": "Vertical offset file",
            "value": "vertcone.94",
            "id": {
                "authority": "EPSG",
                "code": 8732
            }
        }
    ],
    "accuracy": "0.02",
    "scope": "Change of height to a different vertical reference surface.",
    "area": "United States (USA) - CONUS east of 89°W - onshore - Alabama; Connecticut; Delaware; Florida; Georgia; llinois; Indiana; Kentucky; Maine; Maryland; Massachusetts; Michigan; Mississippi; New Hampshire; New Jersey; New York; North Carolina; Ohio; Pennsylvania; Rhode Island; South Carolina; Tennessee; Vermont; Virginia; West Virginia; Wisconsin.",
    "bbox": {
        "south_latitude": 24.41,
        "west_longitude": -89,
        "north_latitude": 48.32,
        "east_longitude": -66.91
    },
    "id": {
        "authority": "EPSG",
        "code": 7971
    },
    "remarks": "In this area the NGVD29 vertical reference surface is approximately 0 to 0.5m above the NAVD88 surface. Interpolation within the gridded data file may be made using either NAD27 or any of the realisations of NAD83 applicable to US conus."
}

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

INSERT into spatial_ref_sys (srid, auth_name, auth_srid, proj4text, srtext) values ( 7971, 'EPSG', 7971, '+proj=vgridshift +grids=us_noaa_vertcone.tif +multiplier=1', 'None');