Galaxy


1. Introduction

This is a demonstration of interactive and collaborative
design of the Milky Way Galaxy, in order to try to fit a
model Galaxy to Earth-based observations of the Milky Way.

The two main display windows of Galaxy show two different
views of the warm (10,000 K) ionized interstellar medium of
the Galaxy. The model of the spatial distribution comes from
an Astrophysical Journal article by Taylor & Cordes (1993,
ApJ 411, 674) using the dispersion measure of pulsars of
known distances. The upper panel shows a 3D isodensity
surface, while the lower panel shows the expected H-alpha
emission integrated out a distance of 6 kpc in all directions
shown in full sky projection.  The peak in the center of the
sky map indicates the large integrated electron density
towards Galactic Center, while the other enhancements in
the galactic plane are due to looking tangentially along
the sprial arms of the Galaxy.

This visualization offers the ability to interactively adjust
the parameters of this model so as to match the observed sky
distribution of ionized gas currently being obtained by Prof.
Ron Reynolds, Dr. Steve Tufte, and Matt Haffner using the
Wisconsin H-alpha mapper (WHAM).

Because of native code, the server and stand-alone modes of
Galaxy run only on Sparc Solaris.


2. Downloading Galaxy

Galaxy is included in the main VisAD distribution.  To
download that, first make sure the current directory is a
directory in your CLASS_PATH.  Then get:

  ftp://iris.ssec.wisc.edu/pub/visad-2.0/visad_src-2.0.tar.Z

or:

  ftp://iris.ssec.wisc.edu/pub/visad-2.0/visad_src-2.0.jar

Unpack the jar file by running:

  jar xvf visad_src-2.0.jar

or unpack the compressed tar file by running:

  uncompress visad_src-2.0.tar.Z
  tar -xvf visad_src-2.0.tar


3. Building Galaxy

Running Galaxy requires VisAD, JDK 1.2 (at least beta4) and
Java3D (at least beta1).  More information about these is
available at:

  http://java.sun.com/

and

  http://www.ssec.wisc.edu/~billh/visad.html

To build Galaxy first edit java/benjamin/Makefile to change
the path:
 
  JAVADIR=/opt/java

to point to the appopriate directory where you installed Java.
Then run 'make' in the visad/benjamin directory.

To build the client mode of Galaxy it is sufficient to run
'javac Galaxy.java' in the visad/benjamin directory.


4. Running Galaxy

Before you run the Galaxy application make sure that your
LD_LIBRARY_PATH includes the visad/benjamin directory (for
access to native code in the shared object libGalaxy.so).
Then run the Galaxy application by typing:

  java visad.benjamin.Galaxy

If you want to run Galaxy in server mode, so that others
can collaborate with you, you must start the rmiregistry
before you run Galaxy.  You can start rmiregistry by typing:

  rmiregistry &


5. Running Galaxy in Client Mode

Before you can run Galaxy in client mode, it must already
be running in server mode (on a Sparc Solaris system with
IP name ip.name.of.server).

Then run the Galaxy application in client mode by typing:

  java visad.benjamin.Galaxy ip.name.of.server


6. How to Operate Galaxy

Galaxy will start with a set of default paramters and
a Milky Way galaxy designed according to them.  It will
take a minute to compute - then an iso-density surface
and an H-alpha emmision sky map will appear in the two
displays.

You can compute different iso-density surfaces by moving
the density slider (drag with the left mouse button) and
pressing the 'Contour button.  You can change the coloring
of the sky map by drawing with the left mouse button in
the color widget.  Clicking the center or right mouse
button cycles through red, green and blue.

To change the galaxy design, adjust the sliders on the
left, and press the 'Compute' button.  Then wait a minute
or two.

You can rotate the displays in the upper window by
clicking the left mouse button and dragging.  Zoom
either of the display windows by dragging the left
mouse button while the SHIFT key is pressed, and pan
any of the four display windows by dragging the left
mouse button while the CTRL key is pressed.

Any changes to the four sliders or to the vertical
profile trigger recomputations, much like a spread
sheet.

In the collaborative mode, all users see the Milky Way
galaxy design.


7. Problems
 
If you have problems, send en email message to the VisAD mailing
list at:
 
  visad-list@ssec.wisc.edu
 
Join the list by sending an email message to:
 
  majordomo@ssec.wisc.edu
 
with:
 
  subscribe visad-list
 
as the first line of the message body (not the subject line).
 
Please include any compiler or run time error messages in the text
of email messages to the mailing list.