Installation instructions are also provided at the ParaView site.

Those instructions suggest that ParaView be installed in /usr/local. If you do this, the various parts of ParaView will be placed in /usr/local/bin, /usr/local/lib, /usr/local/share and /usr/local/doc.

This guide assumes that you have installed ParaView in /usr/local; please adapt accordingly if you have installed ParaView in another location.

3. A Quick Tour

This section will familiarize the reader with ParaView and the basic steps for creating graphics. In the following section, "Tour Redux", these steps will be repeated but with a more thorough discussion of the options.

Before beginning, make sure you have translated at least one MFIX file set to VTK.

3.1 Starting ParaView

Execute /usr/local/bin/paraview.

There are many command-line options, described in Appendix C of the PVG.

3.2 Screen Layout

Chapter 2 of the PVG, "User Interface", includes an excellent description of the layout of the ParaView screen, and should be read someday. However, it is more than is needed to get started and it is slightly out of date. Figure 1 is a simplified and updated description of the screen.

Figure 1. Layout of the ParaView screen (version 2.0.1)
Click on the image for a larger version.

3.3 Reading Data

Select File->Open Data. In the new window, "Open ParaView File", select any one of the VTK files containing a time step. The selected time step will be read into memory and ParaView will know about all of the others when, later, you loop through time.

Once a file is selected, the property sheet area will change to show the sheet for the VTK file reader. Note that the variables found in the data set are listed here and are all on by default. On this sheet, click the green "Accept" button to actually read the data.

The reader will automatically create a simple drawing showing the outer boundary of the data, colored by the first variable.

Moving the mouse around the display area with a button pressed will move the graphic:

• button 1 (typically the left button) rotates
• button 1 plus shift rotates in 2D around the current view direction
• button 2 pans
• button 3 scales

If you get lost, the leftmost button in the Tool Bar, with popup help saying "Reset the view", will move the camera so that the drawing is visible.

Warning: the Tool Bar can be reconfigured and so this button could be absent or in another location.

3.4 Adding A Cut Plane

On the Tool Bar, click on the 6th button from the left, with popup help reading "Cut with an implicit plane".

The property sheet area will change to that for the cut filter. The defaults are reasonable and so click on the green "Accept" button.

Two additional graphics will be added to the display area. One is the 3D plane widget that can be used to move the cut plane. The other is the cut plane itself, colored by the first variable.

Warning: the plane widget can be moved with the mouse. Be careful to click outside this widget to instead move the graphics.

You may notice that the VTK file reader's graphic obscures the cut plane. At the top of most property sheets, there is a list labeled "Selection Window" with an entry for each active module. At this time, there should be two: the reader, with a name taken from the file you selected, and the cut plane, with a name like "Cut1".

The icon to the left of each module name looks like an eye and can be clicked to turn the graphic for that module on and off. Turn off the reader's graphic to see the cut plane.

3.5 Adding An Isosurface

Click the 9th button from the left in the toolbar. Its popup help will read "Generate isolines or isosurfaces". The observant reader will note that nothing happens. Two issues must be addressed to correct this.

The first problem is that each new module takes, as its input, the output of another module. The only exceptions are "sources" such as the VTK reader.

The current module will be the one just added - the cut plane, if you have been following these notes. Using this as input to the contour module will produce 2D contour lines on the cut plane instead of 3D isosurfaces on the data representation. In the "Section Window", click on the VTK reader to make it the current module (the property sheet will change to that for the reader).

The second problem is that MFIX data is attached to the cells while the isosurface module only works with data attached to the vertices. A conversion is required.

Unlike the cut and isosurface modules, the module needed is not on the Tool Bar. The Filter menu on the menu bar displays a comprehensive list of the available filters. Select the filter named "Cell Data to Point Data". Its property sheet will be displayed. Click the green "Accept" button and its drawing will be added in the display area. Since the CellToPoint module is now current, its output will be used for the isosurface.

Try the isosurface button again and click on its green "Accept" button. Turn off the CellToPoint module's graphics to see the new isosurface.

Actually, you still may not see an isosurface because there may be nothing to draw at the current time step, or ParaView's guess at the value may be poor. Changes to time will be discussed next, and the section Adding an Isosurface Redux will discuss changes to the isosurface value.

3.6 Looping Over Time

All looping in ParaView is managed by its animator component. Please read PSC's Using the ParaView Animator for a description of the animator. A few additional details on looping over time are given here.

After creating the desired visualization, expand the animation track for the VTK reader to see the track labeled "FileName". Click twice in this track, once close to the left end and once close to the right end. You have just added two keyframes. Don't worry for now if these are precisely at the start and end of the track; you can edit them later if need be.

Click the animation control button "Play" to step through time.

The default duration for the animation is 10 seconds with 15 frames per second (fps). This works out to 150 frames. If you have more than 150 data time steps, ParaView will randomly skip some.

Alternatively, you can choose a subset of the data time steps to be displayed, or you can change the duration or frame rate to change the number of animation time steps.

ParaView may not be able to update the screen at the requested rate. This can result in not all animation time steps being displayed. The "Play Mode" button in the animation menu offers options in this situation.

The default "Play Mode" is "Sequence", which means that no animation time step will be skipped. In this mode, the animation can take longer than the requested duration to display all the animation time steps. In "Real Time" play mode, the requested frame rate is maintained, but some animation time steps may be skipped.

4. Tour Redux

This section repeats the steps from the previous section but with additional notes and references to the PVG.

Please use Edit->Delete All Modules to begin with a clean environment.

4.1 Screen Layout Redux

What is shown in the main window is controlled from many places.

The menu bar View menu can select between "Source" (usually the current module), the animator, 3D view options (including lookmarks) and general application settings. Turning on the animator display shows both its property sheet, its tracks, and the controls below the tracks.

The menu bar Source menu selects from the modules currently in use.

The menu bar Windows menu controls the display of the property sheet, animation tracks, and parts of the tool bars. Note that the first three tool bar check options control groups of buttons in the main tool bar, while the last controls the set of animation controls shown below the animation tracks.

When viewing a property sheet that shows the "Selection Window", clicking on any module in that list will display that module's property sheet.

For example, screen layout can be configured for a live presentation so that only the display area, Menu Bar and animation controls are shown.

4.2 Reading Data Redux

Select File->Open Data to display the "Open ParaView File" window.

4.2.1 File Formats

Your data can be in any of the file formats supported by your version of ParaView:

• ones described in the PVG's Chapter 3, "Loading Data"
• new formats added after the PVG was written
• formats added by you

ParaView will select the reader using the file extension. Select a file and then click "Open".

4.2.2 Selecting Times

If you wish to select only certain times, or just wish to see what is going on, click the "Timesteps" button on the VTK reader's property sheet. It is at the right end of a group of widgets labeled "Filename", "Browse" and "Timesteps". A popup menu will be shown where the files in the list on the right are the ones that will be read. Edit this list as you wish.

Later, you can return to this option to change the times that are in use. Be sure to click "Accept" for your changes to take effect.

4.2.3 Selecting Variables

Variables will be listed in two groups, though MFIX users only have variables in the Cell Array group. Later, you can return to this option to change the variables that are in use.

4.2.4 Modifying the Reader's Graphic

Select the "Display" tab on the property sheet to change the reader's drawing. As you probably already suspect, all ParaView modules will have a Display tab with the same features.

The "View" group's "Data" button has the same function as the eye button, i.e., it turns the drawing from this module on and off. The "Scalar Bar" and "Cube Axes" enable auxillary display features (try them). The "Label Point Ids" can be useful, or, it can be a big mistake (for large grids). Finally, the "Set View to Data" button can return you to known space if you have become lost.

The "Color" group is useful only if the display style is "Surface" (next group). The "Color by" pulldown menu selects the MFIX variable used to color the surface. The pseudo variable "Property" means you can select a solid color using the "Actor Color" button.

The "Display Style" group lets you select from several "Representations" where most are affected by the other options in this group:

• outline (affected by line width)
• surface (affected by interpolation and opacity)
• wireframe (affected by line width)
• points (affected by point size)
• volume rendering (doesn't work well)

The final group, "Actor Control", only includes one feature that is particularly useful for simple situations: opacity. It only affects the graphic when the representation uses a surface.

4.2.5 Moving the Objects

Moving objects with the mouse is just the start of the many options that control the virtual camera. The PVG's Chapter 6, "Interaction", describes all the options. You may find the section titled "Saving Camera Positions" particularly useful.

The four buttons at the right end of the tool bar affect the center of rotation. These buttons are fairly intuitive. You may have noticed a set of 3D crosshairs in the center of the drawing (change the drawing to Outline or Wireframe to see them). These crosshairs show the center of rotation, and can be turned off.

4.3 Clipping

During the quick tour, all of the data provided by the reader was used. Let's add one additional filter this time to select only a subset of the data (see Figure 2).

Figure 2. The original data (purple) has been clipped using a box (white) and then cut using a plane (green and red).
Click on the image for a larger version.

Click on the Tool Bar button with the popup help saying "Clip with an implicit plane ..." (the 7th from the left). Change the "Clip Function" to "Box", select the "Inside Out" option and then click "Accept".

This has selected the data inside the box, i.e., all of it. Drag the spheres (part of the 3D box widget) to change the size of the box (remember to click "Accept" to see the change). You may need to rotate the drawing to get at some of the spheres.

Once additional drawings have been added (e.g., a cut plane and an isosurface) you may wish to come back to this module to fine-tune the size of the clip box. Any changes to the clipping will cause an update to other modules that use the clip module's output.

4.4 Adding A Cut Plane Redux

First, make sure that the clip module is active so that only the clipped part of the data is used for this cut.

Then, click the 6th button from the left on the Tool Bar, "Cut with an implicit plane", to add the cut module. Click "Accept" to make the cut.

The options on the cut plane's property sheet, under the "Parameters" tab, select the shape, orientation and number of cut planes. The "Display" tab selects the variable used to color the cut. See the section "Modifying the Reader's Graphic", for a discussion of the Display tab.

The PVG's Appendix B, "Filters", includes a discussion of the cut filter along with all other filters.

4.4.1 Multiple Cuts

Multiple cut planes that are parallel to each other and which show the same variable can be created with one instance of the cut module.

However, multiple cut planes using different orientations or showing different MFIX variables will require multiple copies of the cut module. Be sure, when adding additional cut modules, that the clip module is the current module. Otherwise, you will be generating the new cut using only the data selected by a previous cut.

4.4.2 The Cut Function Group

This group of options, on the "Parameters" tab, selects the basic geometry of the cut. A pulldown menu selects between a plane or a sphere. Various other options, concerning location, size and orientation, will be displayed or hidden according to which are appropriate for the selected shape.

When using a plane to make the cut, the mouse (left button down) can be used to move the 3D widget and the cut plane. Drag the widget's arrow to change the plane's normal; drag its rectangular frame to move the cut along its normal. As always, click the green button "Accept" for your changes to take effect.

The plane and sphere widgets, used to move the cut, will be shown only when this module is the current module. In addition, you can use the button at the bottom of this group, labeled "Visibility", to turn the widget on or off. You may wish to turn off the widget to avoid selecting it when you actually want to move the entire graphic display.

4.4.3 The Cut Offset Group

These options, on the "Parameters" tab, set the "offset". For a plane, this is the distance of the cut, along the plane's normal, from the basic cut plane. The default offset is 0, and changing it is no different than moving the basic cut plane.

Use these options if you wish to create a series of cuts by selecting several offsets.

4.5 Adding An Isosurface Redux

First, make sure that the clip module is active so that only the clipped part of the data is used for the isosurface. Then, add the CellToPoint and Contour modules as described in the section "Adding an Isosurface".

Isosurfaces or contour lines are created when the input is 3D or 2D, respectively.

Two variables can be used with an isosurface: the "Scalars" pulldown menu, on the "Parameters" tab, selects the variable used to create the shape of the isosurface, while the "Color by" pulldown menu, on the "Display" tab, selects the variable used to color the isosurface.

Back on the "Parameters" tab, the option groups labeled "Contour Values", "Add value" and "Generate range of Values" are used to set the value(s) used to generate the isosurface. Changing the value, even if you are using only one, is awkward: you must set the new value, add it, delete the old, and then click "Accept".

4.6 Looping Over Time Redux

The PSC guide "Using the ParaView Animator" is a good source of information on animation and looping. The animator is relatively new and subject to change. Currently, the camera location cannot be animated.

The button saying "Save animation as a movie or images" provides a popup menu labeled "Save Animation Images". Use its browser to select the directory and file name for the output. Use the pulldown list for selecting the output format. The MPEG2 format creates a single movie file.

When "Save" is clicked, ParaView will play and record the animation. Warning: anything shown on top of the ParaView display area will be captured as part of the recording.