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3.5 The Field Selector
The Field Selector is used to list the loaded data sources, view their available fields, subset (time and space) the field and create displays. This is normally embedded in the Dashboard but multiple Field Selectors can be shown with the File->New->Field Selector Window menu.
Field Selector Window
Image 1: Field Selector Window
3.5.0 Overview
After choosing some data creating a display is just a couple of steps away:
  1. Click on the data source of interest in the Data Sources list:

  2. Select the field you want to display:

  3. Select the display type:

  4. Optionally subset the times by choosing an option in the drop down menu. See Subsetting for more details.

  5. For grids, optionally subset the levels and/or spatial area:

  6. Press "Create Display":

3.5.1 Data Sources
The left panel shows Data Sources, chosen as described in Choosing Data Sources. You can right click on a data source in the list to show a popup menu:
Data Source Popup Menu
Image 2: Data Source Popup Menu
This allows you to Remove the data source (also by pressing the Delete key), reload its data, show its Properties window, etc.

The Save as Quick Link item will save this data source off as a favorite and make it available in the "Favorite Data Sources" tab of the Quick Links tab of the Dashboard.

3.5.2 Fields
Selecting a data source in the left panel will list the available fields in the Fields tree. This list is usually hierarchical showing different categories of fields (e.g., 2D grids, 3D grids, image sequences, etc.). To see the fields under a particular category click on the toggle icon .

Selecting a field will show the list of displays available in the Displays list and subsetting information (e.g., times, spatial subset).

3.5.3 Subsetting
The "Subsetting" component of the Field Selector allows you to subset the data in both time and space (if possible). If there are times in the data source you are viewing they will be shown in this area. Likewise, if it is possible to do spatial subsetting or decimation a "Spatial Subset" tab will be shown.

Time and spatial subsetting defaults can be applied to the data source itself through the Data Source Properties dialog or the defaults can be overwritten through the Field Selector window.

You can subset the times manually by choosing the Use Selected menu item in the drop down menu and selecting the times. Other options are Match Time Driver and Set As Time Driver. If a user selects the Match Time Driver menu item, the IDV will check the current active view window to make sure there is a time driver available. Otherwise, an error message will appear to remind the user a driver is needed first. When the IDV confirms that a time driver is available, the time list of this dataset will be removed in the subset panel, and the times used by the time driver in the current active display will be used. If a user selects the Set As Time Driver menu item, the selected times of this dataset will be used as the driver times for this view window. Only one time driver is allowed in each view window, and the most recent display set as the time driver will be used.

3.5.4 Creating Displays
The Display tree shows a hierarchical list of the available displays for a particular field. Click on the type of display you want from the choices listed in the Displays tree. You can see examples of Display Types in this Users Guide.

You can select two or more displays (different display types) at one time. For an additional display, hold down the CTRL key and click on the second display type desired. Then go ahead and create the display as normal; all selected displays will be made. To make the display click on the button Create display(or double click on the display).

3.5.5 Derived Parameters
The IDV provides derived parameters -- parameters not provided by the original source data, but made from the source data with computations by the IDV. The intent is to provide commonly used fields such as dewpoint when dewpoint is not provided by the data source, but when it can be derived from source data such as humidity and temperature.

These automatic derived parameters are offered when the required data to compute them are available, based on parameter names.

Since few data sets use the same names for parameters, the IDV keeps of a list of "aliases" or particular parameter names that match with "canonical" names which are generally understood by all IDV users and which the IDV uses for computations. You can add your special parameter names to the list of aliases. Read the Parameter Alias section in this guide for information on using that facility.

All needed source parameters for one derived parameter must come from one single data source, for example, from one single netCDF file. The IDV attempts to find derived parameters that can be made from data in each data source in the data source panel, but not from all possible combination of data sources. If you had separate files of u and v wind components, for example, the parameter names or aliases will not create Derived wind vectors.

3.5.6 Formula Data Source
You can create your own formulas using the IDV Formulas facility. The Formulas data source in the Field Selector is a special data source and lists all of the available end user formulas. You can right-click on the data source to create new formulas and import and export formulas. The formulas are listed in the Fields tree. Right clicking on one of the formulas listed in the Fields tree allows you to edit, copy or evaluate the formula.

You can select a formula just like any other field and create a display from it. However, the formula, when evaluated to create the display, usually needs one or more other data fields to act on. In this case a special Field Selector window is shown that allows the user to select the fields for the formula. (Note: the fields you select here can also be formula fields resulting in further field selection).


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