Web services: NCSS and WCS

This is a blog post about work I’ve done in a past role, but I’d like to get out to a wider audience.

It’s about two different web services that do similar things: NetCDF subset service (NCSS), and Web Coverage Service (WCS). I hope it also helps to act as a short guide on making use of data held at one of Australia’s key research infrastucture assets: the National Computational Infrastructure (NCI).

NCSS is a method for accessing large NetCDF datasets over web endpoints in more or less a ‘lazy loading’ fashion – meaning you can query the data, and set up a processing chain before actually pulling the data to your machinery to do stuff. As far as I’m aware in 2019, the THREDDS data server is the only implementation of NCSS – and as such, if your data are delivered using other methods, it can’t be used. However, if your data sit on a THREDDS server, it is really handy.

WCS is similar in concept – lightweight metadata queries allowing the user to discover things about huge datasets without a huge data transfer penalty. It’s key differences are that it generalises to any raster data format; and has many implementations (THREDDS, Geoserver, Mapserver, …, …); and is an Open Geospatial Consortium (OGC) Standard.

With that very short background, the notebook below shows how the two can be used. It steps through pulling ocean colour data from the same source, using an NCSS strategy and a WCS strategy; and comparing results from the two services.

Feel free to download, use, and play. I’ll update this post with some ideas about how to discover useful data held at NCI sometime in March (2019). For now – this hopes to explain some of the services available; which are generally delivered via a THREDDS data catalogue.

I hope it’s something useful to you!

And of course, I’m happy to to help you develop training materials on geospatial data wrangling and analysis. Look our for more open geospatial training content, and feel free to reach out if you’d like to create bespoke material and have it delivered in person.