Start and End coordinates and depths in DarwinCore

[ValeriedeCarufel]

I work with datasets who are typically structured with start and end coordinates (ex: start and end positions of a trawl event) and start and end depth values (who are not necessarly equivalent to a mininum or maximum depth of the transect) . What would be the best practice to map these informations in the Darwin Core standard?

[ManonGros]

I don't know if there are any best practise for this maybe the OBIS folks would know.

Generally, the start and end position of the trawl event could be modelled in the the dwc:footprintWKT (https://dwc.tdwg.org/terms/#dwc:footprintWKT) field, something like LINESTRING (startLong sartLat, endLong endLat). As far as I know, there wouldn't be something allowing a 3D line. Using the minimum and maximum depth would help make the data findable in GBIF. You can specify more in the samplingProtocol, samplingEffort and eventRemarks fields.

[pieterprovoost]

WKT does allow a third dimension, but you will have to specify what that third dimension is. In this case I think you can use EPSG:9705 (WGS84 + mean sea level height) in dwc:footprintSRS. Here's an example for footprintWKT:

LINESTRING Z (-3.515625 47.709762 -10, -3.779297 45.996962 -100, -4.438477 45.58329 -1000)

[dagendresen]

Maybe it makes sense to create three events - (1) start of the trawl as the first event, (2) the full trawl as the third event, and (3) the end of the trawl as the third event? And chain them together using parentEventID?

[sformel-usgs]

I was unaware of WKT allowing a third dimension, but I think that's a great option for describing the transect. It seems to me that the simplest thing would be to use it to describe the entire transect as a single sample, but I wouldn't be opposed to what @dagendresen suggests, or some variation on it.

[ymgan]

It is also possible to use the extended Measurement or Facts extension (eMoF) for the start and end depth of the Event. Maybe these two vocabs suggested by @JoBeja can be used for measurementTypeID field (if relevant to how they were measured):

• https://vocab.nerc.ac.uk/collection/P01/current/DXPHPRST/
• http://vocab.nerc.ac.uk/collection/P01/current/DXPHPRXN/

Thanks again!