EPSG:9870 - MRH21 Grid + ODN height

{
  "$schema": "https://proj.org/schemas/v0.7/projjson.schema.json",
  "type": "CompoundCRS",
  "name": "MRH21 Grid + ODN height",
  "components": [
    {
      "type": "ProjectedCRS",
      "name": "MRH21 Grid",
      "base_crs": {
        "name": "MRH21-IRF",
        "datum": {
          "type": "GeodeticReferenceFrame",
          "name": "MRH21 Intermediate Reference Frame",
          "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": 9866
        }
      },
      "conversion": {
        "name": "MRH21-TM",
        "method": {
          "name": "Transverse Mercator",
          "id": {
            "authority": "EPSG",
            "code": 9807
          }
        },
        "parameters": [
          {
            "name": "Latitude of natural origin",
            "value": 52.3,
            "unit": "degree",
            "id": {
              "authority": "EPSG",
              "code": 8801
            }
          },
          {
            "name": "Longitude of natural origin",
            "value": -1.8,
            "unit": "degree",
            "id": {
              "authority": "EPSG",
              "code": 8802
            }
          },
          {
            "name": "Scale factor at natural origin",
            "value": 1,
            "unit": "unity",
            "id": {
              "authority": "EPSG",
              "code": 8805
            }
          },
          {
            "name": "False easting",
            "value": 227286.9881,
            "unit": "metre",
            "id": {
              "authority": "EPSG",
              "code": 8806
            }
          },
          {
            "name": "False northing",
            "value": 265751.2874,
            "unit": "metre",
            "id": {
              "authority": "EPSG",
              "code": 8807
            }
          }
        ]
      },
      "coordinate_system": {
        "subtype": "Cartesian",
        "axis": [
          {
            "name": "Easting",
            "abbreviation": "E",
            "direction": "east",
            "unit": "metre"
          },
          {
            "name": "Northing",
            "abbreviation": "N",
            "direction": "north",
            "unit": "metre"
          }
        ]
      }
    },
    {
      "type": "VerticalCRS",
      "name": "ODN height",
      "datum": {
        "type": "VerticalReferenceFrame",
        "name": "Ordnance Datum Newlyn"
      },
      "coordinate_system": {
        "subtype": "vertical",
        "axis": [
          {
            "name": "Gravity-related height",
            "abbreviation": "H",
            "direction": "up",
            "unit": "metre"
          }
        ]
      }
    }
  ],
  "scope": "Engineering survey and topographic mapping for railway applications.",
  "area": "United Kingdom (UK) - on or related to Midland Rail Hub, covering routes through Cardiff, Bristol, Gloucester, Derby, Birmingham, Leicester, and Lincoln.",
  "bbox": {
    "south_latitude": 51.35,
    "west_longitude": -3.27,
    "north_latitude": 53.26,
    "east_longitude": -0.36
  },
  "id": {
    "authority": "EPSG",
    "code": 9870
  }
}

{'crs_wkt': 'COMPOUNDCRS["MRH21 Grid + ODN height",PROJCRS["MRH21 '
            'Grid",BASEGEOGCRS["MRH21-IRF",DATUM["MRH21 Intermediate Reference '
            'Frame",ELLIPSOID["GRS '
            '1980",6378137,298.257222101,LENGTHUNIT["metre",1]]],PRIMEM["Greenwich",0,ANGLEUNIT["degree",0.0174532925199433]],ID["EPSG",9866]],CONVERSION["MRH21-TM",METHOD["Transverse '
            'Mercator",ID["EPSG",9807]],PARAMETER["Latitude of natural '
            'origin",52.3,ANGLEUNIT["degree",0.0174532925199433],ID["EPSG",8801]],PARAMETER["Longitude '
            'of natural '
            'origin",-1.8,ANGLEUNIT["degree",0.0174532925199433],ID["EPSG",8802]],PARAMETER["Scale '
            'factor at natural '
            'origin",1,SCALEUNIT["unity",1],ID["EPSG",8805]],PARAMETER["False '
            'easting",227286.9881,LENGTHUNIT["metre",1],ID["EPSG",8806]],PARAMETER["False '
            'northing",265751.2874,LENGTHUNIT["metre",1],ID["EPSG",8807]]],CS[Cartesian,2],AXIS["(E)",east,ORDER[1],LENGTHUNIT["metre",1]],AXIS["(N)",north,ORDER[2],LENGTHUNIT["metre",1]]],VERTCRS["ODN '
            'height",VDATUM["Ordnance Datum '
            'Newlyn"],CS[vertical,1],AXIS["gravity-related height '
            '(H)",up,LENGTHUNIT["metre",1]]],USAGE[SCOPE["Engineering survey '
            'and topographic mapping for railway applications."],AREA["United '
            'Kingdom (UK) - on or related to Midland Rail Hub, covering routes '
            'through Cardiff, Bristol, Gloucester, Derby, Birmingham, '
            'Leicester, and '
            'Lincoln."],BBOX[51.35,-3.27,53.26,-0.36]],ID["EPSG",9870]]',
 'false_easting': 227286.9881,
 'false_northing': 265751.2874,
 'geographic_crs_name': 'MRH21-IRF',
 'geopotential_datum_name': 'Ordnance Datum Newlyn',
 'grid_mapping_name': 'transverse_mercator',
 'horizontal_datum_name': 'MRH21 Intermediate Reference Frame',
 'inverse_flattening': 298.257222101,
 'latitude_of_projection_origin': 52.3,
 'longitude_of_central_meridian': -1.8,
 'longitude_of_prime_meridian': 0.0,
 'prime_meridian_name': 'Greenwich',
 'projected_crs_name': 'MRH21 Grid',
 'reference_ellipsoid_name': 'GRS 1980',
 'scale_factor_at_central_meridian': 1.0,
 'semi_major_axis': 6378137.0,
 'semi_minor_axis': 6356752.314140356}