Data Selection
Introduction
One of the major design goals of ParaView 3 is to add support for quantitative analysis. In addition to better charting, Python-based filtering and statistical analysis tools, we have been working on the capability of focusing the analysis on a specific subset of a dataset. This can be achieved using the selection mechanism described in this article.
Selection is the mechanism for identifying a subset of a dataset by using user specified criteria. This subset can be a set of point or cells or a block of composite dataset. This functionality allows users to focus on a smaller subset that is important. For example, the elements of a finite-element mesh that have pressure above a certain threshold can be identified very easily using the threshold selection. Furthermore, this selection can be converted to a set of global element ids in order to plot the attribute values of those elements over time.
ParaView supports a single active selection. This selection is associated with a data source (here data source refers to any reader, source or filter) and is shown in every view that displays the data source’s output. This article uses a use-case driven approach to demonstrate how this selection can be described and used. In the next section, we introduce the main GUI components that are used in the article. The subsequent sections address different use cases.
Please note that many features discussed in this article are recent additions and are not available in 3.2. You may want to download a development snapshot or build your own binary from the CVS source base. Otherwise, you will have to wait until 3.4 is out.
Selection Inspector
ParaView provides a selection inspector (referred to simply as the inspector in this article) to inspect and edit the details about the active selection. One can toggle the inspector visibility from the View menu. The inspector can be used to create a new active selection, view/edit the properties of the active selection as well as change the way the selection is displayed in the 3D window e.g. change the color, show labels etc.
We will look at each of these options as we try to explore the different selection types in ParaView.
Spreadsheet View
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Spreadsheet View provides data exploration capabilities. One of the common complaints many users have is not being able to look at the raw data directly. Spreadsheet view provides exactly that. It allows the user to look at the raw cell data, point data or field data associated with a dataset.
ParaView treats spreadsheet view exactly like the other views such as the 3D view, Bar Chart view etc. To create the spreadsheet view, first split the workspace and then choose Spreadsheet View from the options listed. At this time if any source is currently selected in the Pipeline Browser, the spreadsheet view will automatically shows its point data. We can choose the source whose output we want to view using the eyeball in the Pipeline Browser, which is equivalent to turning on the visibility of the source in this view. Spreadsheet view can only show one dataset at a time.
When the spreadsheet view is active (i.e. selected by clicking on its toolbar), and the visible source is selected in the pipeline browser, the Display tab in the Object Inspector panel can be used to control what is shown in this view. This panel contains a selector that can be used to toggle between point and cell data. For composite datasets (multi-block and AMR datasets), it shows a Composite Data Structure tree that can be used to select the block that is shown in the view. Another widget named Show only selected elements can be selected to restrict what is shown in the spreadsheet to only selected cells or points. We will revisit this check box later.
