General Concepts¶
This section explains general concepts and terms regarding xcube Viewer's data model, selections, and layers shown in the map view.
Data Model¶
Dataset¶
In the context of xcube, a dataset is a container for spatial gridded data variables that usually shares the same coordinate reference system, the same dimensions, and therefore the same grid. Besides the data variables, a dataset also provides metadata such as the spatio-temporal coverages, the type of coordinates, and information about the content. A dataset can be associated with place groups.
Datasets that provide variables with two spatial dimensions and a time dimension are also referred to as data cubes. Hence, the data cubes supported by the viewer are 4-D: variable, time, y, and x. The viewer may support also other data cube dimensions in the future.
The list of available datasets is usually fixed for a deployed viewer application instance. One of the available datasets is the viewer's selected dataset.
Variable¶
A variable provides n-dimensional, gridded, geospatial data. Every variable has a name, a numeric data type, and two spatial dimensions. Usually, variables are 3-D and also have a time dimension that can be of variable length. Each time step along the dimension determines an individual 2-D spatial image of the 3-D variable and is associated with a given timestamp.
Places and Place Groups¶
A place represents a region or location that can be associated with data about that region or location. For this purpose a place comprises a name, a geographical vector geometry (point, polygon, etc), and a set of optional data properties.
A place group is a named collection of places.
Places and place groups can be associated with a dataset or
provided by the user. Users can define new places either by drawing points
and shapes into the map. Drawn places end up in special place group
called My places. Or they import custom place groups from GeoJSON
or CSV files.
Selections¶
Selected Dataset¶
The selected dataset determines the set of selectable variables
and the possible range of the currently selected time.
Only one dataset can be selected at the same time.
The selected dataset's time coverage limits the possible values for the
selected time.
If the dataset selection changes, the selected variable
and the selected time may be adjusted if their current values
are not applicable to the newly selected dataset. In this case:
- The newly selected variable will be the first variable of the selected dataset.
- The selected time will be the latest time stamp of the selected dataset.
Selected Variable¶
The selected variable is the one shown in the map, given that the variable layer is visible. Only one variable of a dataset can be selected, but a selected variable may be pinned to allow for inspection of two variables at the same time.
Pinned Variable¶
A pinned variable is a variable that is marked for comparison with
the selected variable.
Only one variable can be pinned at the same time. Note that the
pinned variable does not depend on the selected dataset.
If the dataset selection changes the pinned variable stays the same.
Selected Place¶
One of the available places can be selected by pointing at it on the map. A selected place is required, for example, to compute time-series and statistics. Only one place can be selected at the same time.
Selected Time¶
The selected time determines the current time step for datasets with a time dimension. For such datasets, the selected time is required, for example, to compute statistics.
Layers¶
Variable Layer¶
The variable layer is the top-most gridded data layer in the map. It overlays the dataset RGB layer.
Dataset RGB Layer¶
Some datasets provide an additional RGB layer that can be displayed along with the variable layer. Currently, there can be only be a single RGB layer per dataset.
Basemaps and Overlays¶
The basemap is the layer that is optionally shown below any other layer. The overlay is the layer that is optionally shown above all other layers. Currently, there can be only be a single overlay.