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Subsetting Spatial and Temporal Data

Both the Dataset pane and the Formula pane include the three panels discussed in Sections 9.1 through 9.3: Time Steps, Layers, and Domain, respectively. Section 9.4 then discusses the precedence rules for subsetting data that determine whether Datasets or Formulas take priority.

Specify Time Step Range

The Time Steps panel PDF:[Fig-@fig:Figure24] or GitHub:(Figure 24) displays the range of time steps included in a dataset. The maximum time-step range that can be used for a dataset or formula is specified in the Min and Max spinner controls. You can use these controls to select a subset of the available time-step range for plotting. Check the Use Time Range box above the spinner controls to tell VERDI to use the time-step range values you have specified when it creates a plot. By default, a plot initially displays data for the minimum time step specified in the Time Steps panel. The range of time steps shown in the Time Step spinner control at the top of the plot reflects the subset of time steps specified when the Use Time Range box is checked. The date and time of the time step displayed in the plot are shown below the x-axis labels. Subsetting a dataset’s or formula’s time-step range affect plots produced with those data. Section 9.4 describes the precedence rules.

Figure 24. Specify Time Step Range

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Specify Layer Range

Information on the range of vertical model layers included in a dataset is displayed in the Layers panel PDF:[Fig-@fig:Figure25] or GitHub:(Figure 25) . Use the Min and Max spinner controls to select a subset of the available layer data for plotting. Check the Use Layer Range box above the spinner controls to tell VERDI to use the layers you have specified. By default, a plot will initially display data for the minimum layer chosen in the Layers panel. The range of the layers available in the Layer spinner control at the top of the plot matches the subset of layers specified when the Use Layer Range box is checked. Subsetting a dataset’s or formula’s layer range affects plots produced with those data. Section 9.4 describes the precedence rules.

Figure 25. Edit Layer Range in Formula Pane

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Specify Domain Range

Datasets contain data for cells over a particular geographic area. VERDI refers to this area as a domain. By default, the entire domain contained in a dataset is used in creating plots. Use the Controls menu and then the Set Row and Column Ranges selection to define a subset of this domain for plotting.

Rules of Precedence for Subsetting Data

Use the subsetting feature to combine variables from two or more datasets that originally contained different but overlapping time steps and layers. Select identical subsets of the data available in each dataset such that their time steps and layers match. Then you can select variables from those datasets to create a formula and plot the data. Because both the Dataset pane and the Formula pane have the Time Steps and Layers panels described above, precedence rules determine which pane’s settings take priority. It is important to understand these rules.

NOTE: You must check the appropriate boxes to have your selected ranges take effect.

• Dataset precedence: A subset of data specified in the Dataset pane takes precedence over any subset specified in the Formula pane. However, VERDI does not change the ranges displayed in the Formula pane when you select a subset on the Datasets pane. For example, if a dataset has a full time-step range of 0-48 and you select a time-step range of 2-40 on the Dataset pane, then the 0-48 time-step range that is listed for the formula in the Formula pane is not applicable. When you subsequently create a plot, the time-step range subset you chose in the Dataset pane (2-40) is displayed.

• Formula ranges: If you do not specify a subset for a particular data type (i.e., time steps or layers) in the Dataset pane, then any subsetting for that data type in the Formula pane takes effect.

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