Depth representation conventions

[pbuttigieg]

Linked to #356 and discussions with DECODER (https://github.com/iodepo/odis-arch/blob/schema-dev-df/book%2Fthematics%2Fdepth%2Findex.md) we'll be adding guidance to the ODIS Book on how to represent depth in JSON-LD/schema.org. @fils @pieterprovoost - this is relevant to the discussion just had on how OBIS implements depth. It is vital that something in standard schema.org and/or geoSPARQL is included in the patterns - the world does not speak NERC and those definitions are fragile / ill-posed. This is especially true for CDIF considerations. Such semantics can of course be included if they are accurate and included in the variableMeasured blocks.

[jmckenna]

JSON-LD snippet agreed upon by @fils & @pieterprovoost today, for OBIS depth values:

   "variableMeasured" : [
      {
           "@type": "PropertyValue",
           "name": "maxdepth",
           "description": "Depth (spatial coordinate) relative to water surface in the water body. Definition: The distance of a sensor or sampling point below the sea surface",
           "propertyID": [
               "http://vocab.nerc.ac.uk/collection/P01/current/MAXWDIST/"
           ],
           "measurementTechnique": "description of technique used",
           "unitText": "m",
           "value":  "3456.6"
           "unitCode": [
               "https://qudt.org/vocab/unit/M",
               "https://vocab.nerc.ac.uk/collection/P06/current/ULAA/",
               "http://dbpedia.org/resource/Metre"
           ]
       },
       {
           "@type": "PropertyValue",
           "name": "mindepth",
           "description": "Depth (spatial coordinate) relative to water surface in the water body. Definition: The distance of a sensor or sampling point below the sea surface",
           "propertyID": [
               "http://vocab.nerc.ac.uk/collection/P01/current/MINWDIST/"
           ],
           "measurementTechnique": "description of technique used",
           "unitText": "m",
           "value":  "1234.6"
           "unitCode": [
               "https://qudt.org/vocab/unit/M",
               "https://vocab.nerc.ac.uk/collection/P06/current/ULAA/",
               "http://dbpedia.org/resource/Metre"
           ]
       },
]

[smrgeoinfo]

Vertical CRS are specified in various coordinate system definitions from EPSG: e.g. EPSG:5714 | Orientation: up. Uom: m.

see https://epsg.io/?q=kind%3AVERTCRS+world for a list of defined systems.
Any location that has a vertical coordinate could specific a vertical CRS. Note that for borehole data this might be a linear reference system based on the borehole geometry.

For interoperability, ODIS should recommend/require use of a small set (e.g a depth CRS, an Elevation CRS, depth relative to water surface, vertical coordinate relative to water bottom or ground surface) vertical systems

Note that depth in water or elevation in atmosphere are sometimes measured with a pressure sensor, which is different from a vertical coordinate measured by actual length survey.

[jmckenna]

@smrgeoinfo be careful, epsg.io is no longer maintained. However this old project has been re-activated and is now the recommended one: https://spatialreference.org/ thanks.

[jmckenna]

ODIS partner ZMT pointed to PANGAEA's depth parameter documentation, which is very useful: https://wiki.pangaea.de/wiki/Geocode#DEPTH