EPSG:6917 - SVY21 + SHD height

{
  "$schema": "https://proj.org/schemas/v0.7/projjson.schema.json",
  "type": "CompoundCRS",
  "name": "SVY21 + SHD height",
  "components": [
    {
      "type": "GeographicCRS",
      "name": "SVY21",
      "datum": {
        "type": "GeodeticReferenceFrame",
        "name": "SVY21",
        "ellipsoid": {
          "name": "WGS 84",
          "semi_major_axis": 6378137,
          "inverse_flattening": 298.257223563
        }
      },
      "coordinate_system": {
        "subtype": "ellipsoidal",
        "axis": [
          {
            "name": "Geodetic latitude",
            "abbreviation": "Lat",
            "direction": "north",
            "unit": "degree"
          },
          {
            "name": "Geodetic longitude",
            "abbreviation": "Lon",
            "direction": "east",
            "unit": "degree"
          }
        ]
      }
    },
    {
      "type": "VerticalCRS",
      "name": "SHD height",
      "datum": {
        "type": "VerticalReferenceFrame",
        "name": "Singapore Height Datum"
      },
      "coordinate_system": {
        "subtype": "vertical",
        "axis": [
          {
            "name": "Gravity-related height",
            "abbreviation": "H",
            "direction": "up",
            "unit": "metre"
          }
        ]
      }
    }
  ],
  "scope": "Engineering survey, GIS, topographic mapping.",
  "area": "Singapore - onshore and offshore.",
  "bbox": {
    "south_latitude": 1.13,
    "west_longitude": 103.59,
    "north_latitude": 1.47,
    "east_longitude": 104.07
  },
  "id": {
    "authority": "EPSG",
    "code": 6917
  }
}

{'crs_wkt': 'COMPOUNDCRS["SVY21 + SHD '
            'height",GEOGCRS["SVY21",DATUM["SVY21",ELLIPSOID["WGS '
            '84",6378137,298.257223563,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]]],VERTCRS["SHD '
            'height",VDATUM["Singapore Height '
            'Datum"],CS[vertical,1],AXIS["gravity-related height '
            '(H)",up,LENGTHUNIT["metre",1]]],USAGE[SCOPE["Engineering survey, '
            'GIS, topographic mapping."],AREA["Singapore - onshore and '
            'offshore."],BBOX[1.13,103.59,1.47,104.07]],ID["EPSG",6917]]',
 'geographic_crs_name': 'SVY21',
 'geopotential_datum_name': 'Singapore Height Datum',
 'grid_mapping_name': 'latitude_longitude',
 'horizontal_datum_name': 'SVY21',
 'inverse_flattening': 298.257223563,
 'longitude_of_prime_meridian': 0.0,
 'prime_meridian_name': 'Greenwich',
 'reference_ellipsoid_name': 'WGS 84',
 'semi_major_axis': 6378137.0,
 'semi_minor_axis': 6356752.314245179}