Multidimensional

Multidimensional data is held in HydroShare using Network Common Data Form or NetCDF files.  Multidimensional space-time data is commonly used for hydrological modeling. For example, precipitation or surface air temperature can be recorded as a multidimensional space-time dataset with two dimensions in space and one dimension in time.

NetCDF files contain self-describing metadata and support the creation of an array-oriented dataset, which may include three spatial dimensions, a time dimension and other user defined dimensions. A Multidimensional (NetCDF) content aggregation is created from a single NetCDF file with a “.nc” file extension. HydroShare uses ncdump -h (a NetCDF utility function) to extract the self describing header information from this file and saves the resulting header file alongside the content aggregation a folder. 

While any NetCDF file can be used in HydroShare, we encourage the use of Climate and Forecast (CF) and ESIP Attribute Convention for Data Discovery 1-3 ACDD conventions.  HydroShare matches metadata from the header file with CF and ACDD convention tags to identify and populate content aggregation and resource metadata.  Thus when a NetCDF file with author, keyword, spatial and temporal reference and other matched metadata is imported to HydroShare, there is no need for a user to enter this information, simplifying the process for a user.

Example

An empty composite resource is created.  A NetCDF file is added by dragging into the content area


HydroShare recognizes this as a NetCDF file and reads metadata from it, and sets the resource level Title, Abstract, Authors, Keywords and Coverage based on this metadata.  Multidimensional content is stored in a folder depicted using a multidimensional symbol

In addition to the .nc file the multidimensional content contains *header_info.txt that is the result of a NetCDF header dump (ncdump -h) of the file that may be viewed in the Content Metadata tab.

Metadata extracted from this netCDF file populates the content aggregation level title, keywords and coverage as illustrated below

The metadata panel also shows the full NetCDF header file

Metadata is also propagated up to the resource level to the Title, Authors, Abstract, Keyword and Spatial coverage metadata.

The following resource holds the file used in this example https://doi.org/10.4211/hs.f3f947be65ca4b258e88b600141b85f3

CF and ACDD terms recognized by HydroShare

The table below displays the mapping of terms between the HydroShare metadata and NetCDF CF and ACDD conventions.

HydroShare

NetCDF conventions

creator: name

creator_name (ACDD)

creator: url

creator_url (ACDD)

creator: email

creator_emal (ACDD)

contributor: name

contributor_name (ACDD)

coverage (temporal): start

time_coverage_start (ACDD)

coverage (temporal): end

time_coverage_end (ACDD)

coverage (spatial): north latitude

geospatial_lat_max (ACDD)

coverage (spatial): south latitude

geospatial_lat_min (ACDD)

coverage (spatial): east longitude

geospatial_lon_max (ACDD)

coverage (spatial): west longitude

geospatial_lon_min (ACDD)

abstract

summary (ACDD)

relation: cites

references (ACDD)

license

license (ACDD)

source

source (CF)

subject

keywords (ACDD)

title

title (ACDD)

Variable: unit

unit (CF)

Variable: long name

long_name (CF)

Variable: missing value

missing_value (CF)

Variable: comment

comment (CF)

Spatial Reference: coordinate reference system

grid_mapping_name (CF)

Spatial Reference: Coordinate String, Coordinate String Type, Datum

attributes for grid mapping variable (CF)

Update Metadata in the NetCDF File

HydroShare enables interactive editing for the NetCDF file metadata and the resource specific metadata on the resource landing page within the metadata panel. If a user makes changes to the resource specific metadata, a warning will appear at the top of the metadata panel that says the “NetCDF file needs to be synced with metadata changes” in which case the user can click “Update NetCDF file” (shown below) to update the NetCDF file metadata.

OPeNDAP Web Services

OPeNDAP web service enables users to access and subset NetCDF files stored in HydroShare through an OPeNDAP data access form in a web browser or using OPeNDAP client software for data visualization or analysis. This will allow the user to easily create or visualize a subset dataset from the original NetCDF file without downloading the file from HydroShare to local computers.

OPeNDAP services are automatically enabled for resources with multidimensional netCDF content that are made Public.  To make a resource Public use the Manage access panel accessible from the toolbar at the top of the resource

And set Sharing status to Public

Then any user accessing this resource should find the “OPeNDAP” web app by clicking on “Open with” button at the top of the resource

and access the OPeNDAP data service for this resource. To disable the OPeNDAP service, the set the resource as “Private” or “Discoverable”.