INTERACTIVE VISUALIZATION OF COMPUTATIONAL FLUID DYNAMICS USING MOSAIC

Jean Clucas
Software Specialist
Sterling Software, NASA Ames Research Center

Velvin (Val) Watson
Senior Staff Scientist
NASA Ames Research Center

July, 1994

• A Scientific Expedition
  • The Visualization Tool: FAST (Flow Analysis Software Toolkit
  • Using FAST for Scientific Expeditions
• Developing the Implementation for Ease-of-Use and Security
  • FASTtrek Implementation Overview
• Comparison of Using Movies and FAST Expeditions
  • Movies of Ocean Currents
  • FAST Expeditions into the Ocean Currents
  • Comparison of the Features
• Other Features
  • Remote Collaboration
  • Creating Scientific Expeditions for use with FAST
• The National Goals

A Scientific Expedition

• To make scientific data itself, rather than pixel image files, available, along with tours through the data and the capability for further analysis by the user.
• To provide this capability with easy-to-use, standardized tools.
• To do this with tools that use network bandwidth more intelligently.
• To propose that putting these tool in every high school before the end of 1996 be a national goal.

The Visualization Tool: FAST (Flow Analysis Software Toolkit) (1)
FAST is a software package for the visualization of three-dimensional data, particularly Computational Fluid Dynamics data. It provides a variety of methods for examining data, such as plotting flow paths around an aircraft, color-mapping temperature on the surface, locating areas of a specified pressure, displaying vectors, and finding vortices. When a view or views are found which reveal important features of the data, an image can be generated, or an animation created.


FAST on HDTV Monitor.(2)
This image is from a visualization created by FAST. Clicking on the image will link you to a file of FAST-generated images (and one mpeg animation) on the NAS (Numerical Aerodynamics Simulation Division) Web server at NASA Ames.

Each time FAST is used, the session is recorded to file as a series of commands. This feature allows scientists to reexamine data they have viewed previously in FAST, without repeating the process of loading data and stepping through the commands previously issued. This is also the feature which makes FAST easily adaptable to use on the Web. Rather than putting an animation online, we are proposing that scientists share the entire FAST session, and thus the possibility for further analysis, with the scientific community. Because FAST can be driven by a script, the minimum necessary to do this is simply making the dataset and script available from HTML documents. What we propose, however, is the integration of Scientific Expeditions into Mosaic sessions, using visualization tools like FAST as data "viewers," in the sense that xv is an image viewer for Mosaic.

Using FAST for Scientific Expeditions
We have made some sample scientific expeditions available. They can be run by anyone who has a Silicon Graphics workstation, and the FAST software. Plans for making FAST available via Mosaic are being developed. It may or may not be available by the Web conference date. At present, it is available via COSMIC. The method for obtaining FAST will be kept current on the FAST home page. See How to Get FAST or the FAST home page (1) if you need to obtain the software. This document provides links to the utilities needed to integrate FAST Expeditions into Mosaic and takes the reader through one expedition. Other Expeditions will be placed at FAST's Expeditions URL (3) as they are developed.

The expeditions integrate FAST into Mosaic by defining FAST-related files as a mime type, x-fasttrek, which is returned for files with the suffix .FASTtrek. .FASTtrek files are passed to a shell script (called FASTtrek) which handles the details of sorting out datasets and scripts, making security checks, and sending the data and scripts to FAST. From the user's point of view, one simply clicks on a link, and the viewer, FAST, pops up and displays an animation, just as any other viewer displays its image or animation. But this viewer has advantages over other viewers:


• More information is transmitted while using less bandwidth.
• The actual dataset is transmitted along with the guided expeditions, which permits the scientist or student to do further analysis.
• The scripting feature also allows interactive sessions, in which scientists at remote locations can view data simultaneously, passing control of the display back and forth. We use the term Remote Collaboration to describe this two-way interaction.

Scripting
In a later section, we will compare a set of 30 MPEG animations to using FAST to view the same data. With that dataset, each MPEG animation is about two megabytes, which is more than 60 megabytes for the 30 movies, while the entire FAST Expedition is less than one megabyte, contains more information than all 30 movies, and offers the user the ability to interact with the data. The FAST script files used for animations are very small, since they consist of a series of commands like the following:
file_IO: READ_FILE grid.bin
file_IO: FILE_TYPE FUNCTION
file_IO: READ_FILE scalar_field.bin
surfer: TYPE SCALAR
The above lines are sufficient to load a three dimensional grid of, for example, an aircraft, and a file containing values for pressure on the surface and in the surrounding space, and then display the surface of the aircraft with pressure color-mapped onto it.
surfer: NEW_OBJECT
surfer: DIRECTION I
surfer: RENDER CONTOUR_LINES
surfer: LOOP FORWARD
This second set of commands creates a simple animation through the pressure field surrounding the aircraft, similar to the animation used to create the pictures from a FAST animation shown below in the "FASTtrek Implementation Overview."

A second reason for deciding on a different approach was our goal of creating an easy-to-use, full-featured standard tool as a data "viewer" for Mosaic. This included providing a graphical user interface, and allowing for Remote Collaboration, the simultaneous viewing of a FAST session at multiple sites, with swapping of control. Therefore, we created a set of executables to be installed on each user's machine. We continued development with an awareness of the security risks inherent in a tool that permits users to bring groups of files to their machines, and run them without inspecting them. We found two risks specific to our implementation:

• The files sent in a FASTtrek could contain an executable with an innocuous name, such as "fast," which could be invoked by users who have their current directory in their path. We prevent this by having FASTtrek check for the location of FAST before extracting the files, and by using absolute path names.
• It is possible to send a system command from a FAST script. FASTtrek searches and deletes any system commands from scripts it sends to FAST. While this removes one feature from FAST, it seems an acceptable sacrifice in the name of security.

• Load an archive file that can be run as a C shell script which unloads its own contents, the FASTtrek executables. This script also modifies the user's .mailcap and .mime.types files, and notifies the user of any missing elements in the configuration (such as not finding FAST in the executable path). To do this, select Options/Load to Local Disk, and copy FASTarchive.csh to a directory in your executable path. Then, in a shell window, cd to the directory and type
  csh FASTarchive.csh
  When installation is complete, select Options/Reload Config files and you will be ready to run FAST Expeditions.

• For those preferring to inspect and control any changes made to their machine, several approaches exist:
  • The C shell script that unpacks the archive is a short, simple set of commands at the head of the file, which can be examined;
  • The source files can be inspected or copied individually, or the executables can be copied individually: See FASTtrek Executables. Users of this approach will need to modify their own .mailcap and .mime.types files.
  • One can simply copy the FASTtrek executable, a C shell script, by itself. It allows users to run Scientific Expeditions, but Remote Collaboration and the GUI will not be available. Users will need to modify their .mailcap and .mime.types files.

• A tarred, gzipped file containing data and one or more FAST scripts. When one of these files is read, FASTtrek unpacks the files, creates a subdirectory in a standard location for storing the script files, creates several other files in the subdirectory, and starts FAST with the script designated as the startup script, which reads the data and prepares for the Expeditions.

  
  FASTtrek reads an archive containing data and scripts, and starts FAST with a setup script, which loads the data and prepares for the Expeditions.

• A single FAST script. In general, all the scripts associated with a particular dataset are sent with the dataset, and placed in a subdirectory of /tmp. The html document should contain links to this location. Additional scripts for FASTtreks can be developed and made available individually. Each script must contain the line: #FASTtrekscript [scriptname].FASTtrek in order to be recognized by FASTtrek. When using the utility for assembling a dataset into a FAST Expedition, this line is added automatically. If the script is created separately the line must be added by hand.

  
  Scripts for viewing the dataset (4), are a second FASTtrek type. The images here are from a FAST script animation that sweeps a plane of pressure contours through the data.

• Files containing a command to be performed. These include exiting FAST, saving the data used in the FAST Expedition to a permanent directory, cleaning up temporary files, and running a Remote Collaboration session. These files are created under /tmp when the dataset is read, and are used to control the FASTtrek with hyperlinks. A hyperlink to /tmp/FASTexpeditions/FASTexit.FASTtrek, for example, will send a file containing the single line "FASTexit" to the FASTtrek executable, which will then terminate FAST.

  
  When FASTtrek loads a dataset, it creates a third type of .FASTtrek file: temporary files containing commands, which are stored in a standard location. Links to these files on the HTML document provide an interface to FAST.

Movies of the Ocean Currents
The Acoustic Doppler Currents Profile (5)MPEG movies in the Example Movies of Scientific Data illustrate the current trend to display animated data in compressed pixel form. Each movie contains a currents profile, displaying the direction and speed of currents at 30 depth levels in the ocean. The direction of currents is represented by arrows, and the arrows' length and color represent the speed of the current. Each MPEG animation represents one profile, and each movie requires the transfer of approximately 2 MBytes of data for 89 frames of movie.

FAST Expeditions into the Ocean Currents
To compare with the movies above, we have generated a similar dataset for viewing with FAST. However, our dataset contains 30 days of velocity profiles (the equivalent of 30 movies). This FAST Expedition begins by displaying the velocity vectors colored by the magnitude (as in the movie), but it is not limited to this mode of display.

In addition to the guided expeditions below, you can elect to conduct your own expedition into this data. For example, you could view the day-of-month vs. time-of-day surfaces while sweeping through the depth direction, or you could view the depth vs. time-of-day surfaces while sweeping through the day-of-month direction. (The time-of-day dimension has been compressed to make a close comparison to movies. You may wish to re-expand it.)

You can sequence the guided expeditions in interesting ways. We recommend the "Time sweeping on" followed by the "Stereo". The "viewing as a surface that goes though the ends of the vectors" followed by the "Initiate a flyby ..." is also interesting - it permits viewing the correlation of velocity profiles from day to day.

The Stereo mode is for use with Crystal Eyes glasses.

Load the Data and Prepare for the Expeditions
Please wait for the prompt to "try an expedition" before selecting each option
Guided Expeditions


• Time sweeping on - This permits viewing as a movie through time
  This is the mode that compares directly with the movies. While the movie is playing, try rotating to get a better view of 3D. Also, try panning through the days of the month. If you lose the picture off the screen, reset the view.
• Reset the view to the original position.
• Time sweeping off - This stops viewing as a movie through time
• Reset the time of day to zero
• View the surface that goes through the ends of the vectors
• Initiate a flyby over the depth vs. day-of-month surface
• Stop the flyby over the depth vs day-of-month surface
• Go back to viewing the plain vectors
• Stereo - This creates a full screen stereo image for use with Crystal Eyes.
  NOTE! - when through viewing the stereo scene, press ENTER to exit from full screen mode
• Mono - This returns from stereo to mono

Exit the FAST scientific visualization program
Save the data and expeditions in a local directory for later use
Remove all temporary files used by the FAST Expedition

Comparison of the Features
The FAST Expeditions to explore equivalent data illustrate

• The data to be transferred can be reduced dramatically: the entire FAST Expedition, containing the equivalent of 30 movies, is less than half the size of one MPEG movie. Therefore, the volume of data sent over the net was reduced by nearly 2 orders of magnitude.
• The viewer can view the data in a much richer variety of ways.
  • The data can be viewed in 3D to see the direction of the vectors. One cannot tell the direction of 3D vectors in space with a single view (as in the movies). With FAST, one can rotate the viewing position to determine the direction of the 3D vectors. (Running the Stereo script, for use with Crystal Eyes stereo glasses, one can determine the direction of the vectors without rotating the view.)
  • All of the data in the movies can be viewed at once to better view correlations in the various dimensions (depth, day, and time of day).
  • In addition to "sweeping through time" as in a movie, the viewer can sweep through the other dimensions.
  • The viewer can interactively highlight features through color selection and other techniques.
• The viewer can do his own "what if" analysis of the data.

Other Features

Remote Collaboration (6)
When FASTtrek is passed a file containing the command FASTremote, it creates a pipe from which FAST will read script commands. It also creates files containing the commands FASTmaster, FASTconnecttomaster, and FASTdisconnect, to control FASTtrek. When a user becomes master, and other users connect, FASTtrek calls the utilities FASTtalkserver and FASTlistento, to create socket connections between the machines. FASTtalkserver reads FAST commands as they are generated by FAST, and sends them to the slave machines, where FASTlistento handles receiving the commands and piping them to FAST.

From the user's point of view, the only technical hurdle is inserting a line in the /etc/services file (which requires root privileges):
fastd 5001/tcp
Once that is done, to run a collaborative session one simply clicks on FAST remote, then on FASTmaster or FASTconnecttomaster. To switch, the user clicks on the other choice. Clicking on FASTdisconnect severs connections.

The simplicity of this interface makes using Mosaic desirable for remote collaboration any time remote collaboration is done, and not only for connecting with scientists supplying FAST Expeditions on the Web. For local use, an html page linked to a FASTremote file and to the /tmp location where FASTtrek will put FASTmaster and FASTconnecttomaster is provided in the archive.

To try Remote Collaboration, you must have the entry in /etc/services described above. Then, contact a colleague. Each Collaborator should run FAST, load the same data, and then select Initialize FAST Remote. When remote setup is initialized, select from:

• Become Master
• Connect to Master
• Sever Connections
• FASTexit
• FASTcleanup

Creating Scientific Expeditions for use with FAST

For users running web servers, creating FAST expeditions is easy. A nawk script, FASTtar.nawk, is provided. To create an expedition, invoke FASTtar.nawk, passing it the names of the FAST scripts for the expedition. The nawk script will create soft links to the datasets read by the scripts, and assemble all the scripts and the data in a gzipped tar file. If Remote Collaboration is desired, a FASTremote file can be included. In addition to creating the FASTtrek file, the nawk script makes a skeleton home page with hyperlinks to the scripts already on it.

These FAST Expeditions were developed in support of a proposal to the NSF, NCSA, and NCGA to define the Scientific Expeditions as a way to improve use of the information superhighway, and to bring Scientific Expeditions into the schools. Specifically, the goals are:

The Proposed Target


A capability as good or better than the FAST Expedition approach outlined here.

Proposed National Goals


Goal 1

The "scientific expedition" shall be available to

• Every high school and above by the end of 1996
  
• Every school by the end of 1998

Goal 2

NASA, EPA, and similar research facilities, shall have information available on the Information Superhighway in a format like the Scientific Expedition by the end of 1996.

To learn more about FAST Expeditions and the National Goals, see the National Goals Home page.

Notes

1. Flow Analysis Software Toolkit (FAST) is currently under development by members of the Numerical Aerodynamics Simulation (NAS) Division at NASA Ames Research Center, Moffett Field, CA 94035-1000. See the FAST home page for information on FAST, including how to get FAST. The URL is:
   http://www.nas.nasa.gov/FAST/fast.html
   
2. FAST on HDTV Monitor. Visualization by John West, FAST Development Team, Sterling Software, Inc. Grid and solution courtesy of Dr. David Huddleston and Dr. Bharat Soni, NSF Engineering Research Center for Computational Field Simulation, Mississippi State University.
3. The FAST Expeditions, the Web location where new Expeditions are being placed, is
   http://www.nas.nasa.gov/FAST/Expeditions
   
4. The animation shown is from Effect of a Canard on Vortex Structure and Pressure by Eugene L. Tu, RFA/NASA Ames.
5. Acoustic Doppler Currents Profile (ADCP) MPEG movies are produced daily by Cheng Tang for the REINAS project at University of California, Santa Cruz. These movies display ocean currents profile data collected from MBARI's M1 buoy, data courtesy of Dr. L. Rosenfeld.
6. The Remote Collaboration technology was developed by Val Watson and John West.

Jean Clucas

Ms. Clucas has 10 years experience as an educator, most recently as an instructor in computer graphics and animation for the Computer Technology and Information System Division at Foothill College, Los Altos California.

Mail Stop T27a-2
NASA Ames Research Center
Moffett Field, CA 94035-1000

Phone: (415) 286-5761
email: clucas@nas.nasa.gov

Val Watson

Val has also been active in promoting the use of computers in teaching and in professional society presentations. He has been using computers for live illustrations in presentations and classroom lectures since his 1979 pioneering use of computers for live illustrations in computational fluid dynamics courses over the Stanford Instructional Television.

Val has been chairman of the Interactive Computer Graphics Technical Committee for the American Institute of Aeronautics and Astronautics and is currently a member of the Board of Directors of NCGA. He received a BS in Mechanical Engineering and MS in Aeronautics from UC Berkeley, and a PhD in Aeronautics and Astronautics from Stanford University.

Mail Stop 258-2
NASA Ames Research Center
Moffett Field, CA 94035-1000

Phone: (415) 604-6421
FAX: (415) 604-4377
email: watson@nas.nasa.gov
URL http://www.nas.nasa.gov/FAST/Nationalgoals/watson.html