Is this a DAP2 or DAP4 URL?#
Only two OPeNDAP servers broadly support DAP4: Hyrax Data Server (developed by OPeNDAP Inc, the original architects of OPeNDAP), and Thredds Data Server (developed by NSF Unidata). DAP4 was originally developed jointly by OPeNDAP and Unidata back in 2016 (see the DAP4 specification). Any Hyrax and Thredds servers that implements DAP4 also implements the DAP2, and checking whether a URL is DAP4 or DAP2 is different with each of this servers.
Hyrax Data Server#
With Hyrax, the easiest way to check if the url supports DAP4 or not, is to take the URL, append a .dmr (or .dmr.html), and past it onto a browser. For example, consider the following Hyrax opendap URL
URL = http://test.opendap.org/opendap/data/nc/coads_climatology.nc
Note
A Hyrax server that implements DAP4 should implement DAP2. In most Hyrax servers (version > 1.15) DAP4 is the default protocol implementation, and when a user requests a DAP2 response, the server first processes and then translates a DAP4 into a DAP2 response. This enables backwards compatibility with older clients that can only parse DAP2 responses, while supporting newer datasets. In the process of doing so, it is possible that the remote dataset cannot be translated into a DAP2 response in its entirety, and the Hyrax can return a 400 Error instead (see word of caution)
Warning
To see the latest official release of Hyrax, go to the official OPeNDAP website and check Latest Release under Software.
Thredds Data Server#
With the TDS, a DAP2 URL will have a dodsC on its URL. If you replace the dodsC with dap4, and past it onto a browser it should produce a produce a webpage that allows to download a DAP4 response. For example, consider the
URL = https://thredds-test.unidata.ucar.edu/thredds/dodsC/testdods/coads_climatology.nc
Warning
A Thredds server that implements DAP2 may not implement DAP4. It is strongly recommended to check if a server is configure to offer the DAP4 endpoint.
Note
To see the latest official release of Thredds, go to the official Thredds page.