EPSG:5739 — HKCD depth

VERTCRS[
    "HKCD depth",
    VDATUM["Hong Kong Chart Datum",ID["EPSG",5136]],
    CS[vertical,1,ID["EPSG",6498]],
    AXIS["Depth (D)",down],
    LENGTHUNIT["metre",1,ID["EPSG",9001]],
    ID["EPSG",5739]
]

+vunits=m +no_defs +type=crs

proj4.defs("EPSG:5739", "+vunits=m +no_defs +type=crs");

{
  "type": "CoordinateReferenceSystem",
  "code": 5739,
  "name": "HKCD depth",
  "kind": "vertical",
  "area": "Hong Kong - offshore",
  "unit": "metre",
  "bbox": [
    22.13,
    113.76,
    22.58,
    114.51
  ],
  "proj4": "+vunits=m +no_defs +type=crs"
}

INSERT INTO spatial_ref_sys (srid, auth_name, auth_srid, proj4text, srtext)
VALUES (5739, 'EPSG', 5739, '+vunits=m +no_defs +type=crs', 'VERT_CS["HKCD depth",VERT_DATUM["Hong Kong Chart Datum",2005,AUTHORITY["EPSG","5136"]],UNIT["metre",1,AUTHORITY["EPSG","9001"]],AXIS["Depth",DOWN],AUTHORITY["EPSG","5739"]]');

PROJECTION
  "+vunits=m"
  "+no_defs"
  "+type=crs"
END

5739=VERT_CS["HKCD depth",VERT_DATUM["Hong Kong Chart Datum",2005,AUTHORITY["EPSG","5136"]],UNIT["metre",1,AUTHORITY["EPSG","9001"]],AXIS["Depth",DOWN],AUTHORITY["EPSG","5739"]]