Identifying vertical datum of raster

Question

I have a DEM that purports to use the Canadian Geodetic Vertical Datumn 1928 (CGVD28) where heights are normal-orthometric.

However, when I run gdalinfo dem.tif from the command line the output for DATUM is "WGS 84"

Driver: GTiff/GeoTIFF
Files: dem.tif
Size is 8209, 7899
Coordinate System is:
PROJCRS["WGS 84 / UTM zone 9N",
    BASEGEOGCRS["WGS 84",
        DATUM["World Geodetic System 1984",
            ELLIPSOID["WGS 84",6378137,298.257223563,
                LENGTHUNIT["metre",1]]],
        PRIMEM["Greenwich",0,
            ANGLEUNIT["degree",0.0174532925199433]],
        ID["EPSG",4326]],
    CONVERSION["UTM zone 9N",
        METHOD["Transverse Mercator",
            ID["EPSG",9807]],
        PARAMETER["Latitude of natural origin",0,
            ANGLEUNIT["degree",0.0174532925199433],
            ID["EPSG",8801]],
        PARAMETER["Longitude of natural origin",-129,
            ANGLEUNIT["degree",0.0174532925199433],
            ID["EPSG",8802]],
        PARAMETER["Scale factor at natural origin",0.9996,
            SCALEUNIT["unity",1],
            ID["EPSG",8805]],
        PARAMETER["False easting",500000,
            LENGTHUNIT["metre",1],
            ID["EPSG",8806]],
        PARAMETER["False northing",0,
            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]],
    USAGE[
        SCOPE["Engineering survey, topographic mapping."],
        AREA["Between 132┬░W and 126┬░W, northern hemisphere between equator and 84┬░N, onshore and offshore. Canada - British Columbia (BC); NorthW Territories (NWT); Yukon. United States (USA) - Alaska (AK)."],
        BBOX[0,-132,84,-126]],
    ID["EPSG",32609]]
Data axis to CRS axis mapping: 1,2
Origin = (559006.126505142310634,5824083.277645028196275)
Pixel Size = (25.087306974829975,-25.087306976783019)
Metadata:
  AREA_OR_POINT=Area
Image Structure Metadata:
  INTERLEAVE=BAND
Corner Coordinates:
Upper Left  (  559006.127, 5824083.278) (128d 7'46.21"W, 52d33'48.99"N)
Lower Left  (  559006.127, 5625918.640) (128d 9'46.81"W, 50d46'55.26"N)
Upper Right (  764947.829, 5824083.278) (125d 5'45.62"W, 52d30' 8.58"N)
Lower Right (  764947.829, 5625918.640) (125d14'44.98"W, 50d43'28.39"N)
Center      (  661976.978, 5725000.959) (126d39'30.55"W, 51d39' 9.49"N)
Band 1 Block=8209x1 Type=Int32, ColorInterp=Gray
  NoData Value=-2147483647

If this is telling me the horizontal datum only, how do I confirm the vertical datum?

Answer 1

If the metadata specified a vertical datum it would appear as a VERT_CS section in the WKT like:

COMPD_CS["ETRS89 / NTM zone 14 + NN2000 height",
    PROJCS["ETRS89 / NTM zone 14",
        GEOGCS["ETRS89",
            DATUM["European_Terrestrial_Reference_System_1989",
                SPHEROID["GRS 1980",6378137,298.257222101,
                    AUTHORITY["EPSG","7019"]],
                TOWGS84[0,0,0,0,0,0,0],
                AUTHORITY["EPSG","6258"]],
            PRIMEM["Greenwich",0,
                AUTHORITY["EPSG","8901"]],
            UNIT["degree",0.0174532925199433,
                AUTHORITY["EPSG","9122"]],
            AUTHORITY["EPSG","4258"]],
        PROJECTION["Transverse_Mercator"],
        PARAMETER["latitude_of_origin",58],
        PARAMETER["central_meridian",14.5],
        PARAMETER["scale_factor",1],
        PARAMETER["false_easting",100000],
        PARAMETER["false_northing",1000000],
        UNIT["metre",1,
            AUTHORITY["EPSG","9001"]],
        AUTHORITY["EPSG","5114"]],
    VERT_CS["NN2000 height",
        VERT_DATUM["Norway Normal Null 2000",2005,
            AUTHORITY["EPSG","1096"]],
        UNIT["metre",1,
            AUTHORITY["EPSG","9001"]],
        AXIS["Up",UP],
        AUTHORITY["EPSG","5941"]],
    AUTHORITY["EPSG","5954"]]

as seen in http://epsg.io/5954

Note this is a compound coordinate system with a 2d geographic system and a vertical system.

Your metadata there does not specify a vertical coordinate system. I suppose its possible there's another TIFF tag with it in, but I would have expected gdalinfo to know about it.

You could possibly construct the compound system from the geographic system you have and the string for your vertical system (epsg vertical datum 5114 it seems http://epsg.io/5114-datum ) and save that back into your data for future reference. That's if you believe the data is already of that datum...

The only way to "confirm" the height datum would be to compare the heights in your data with known-certain heights from the same datum via another source.