| The ToyFDTD FAQ |
Viewing
mpeg movie files Dealing
with .tar and .gz files About
the animations' colormapping Autoscaling
vs. global scaling C-F90
floating point differences Sanity
Savers & FDTD
Viewing mpeg movie files: You
can download a file to a directory on your machine, and then use
whatever mpeg viewer you have to play it. Or you can set your browser
to view them automatically. Here's how I did it on mine (Netscape):
In the popup box click the arrow next to Navigator to show the submenus
Choose Applications
Scroll down until you see MPEG Video, then click on whatever appears next to it under "handled by" and hit "edit"
Click on Application
Type in the command to activate your movie player, and hit the OK buttons
-- I used: mpeg_play -quiet -dither color %s
An important note: be sure that the movie player you use has its play all frames option set. Some mpeg players assume that the file includes audio, so they skip frames to keep up with the imaginary audio track. This will make ToyFDTD animations look jerky.
Dealing with .tar and .gz
files:The
tar files each contain several files within them. If you have a tar
file with a name ending in .tar, you use a command like
tar xvf filename.tar
to un-tar it, which will give you a new directory named filename which will contain all the files included in the original tar file. You can now do whatever you want with them.
If your tar file name ends in .tar.gz, that means it is compressed for faster downloading. To un-compress a your filename.tar.gz, use a command like
gunzip filename.tar.gzThis will give you filename.tar which you can un-tar as just explained. The commands given here are Unix commands, if your computer uses a different operation system, you'll want to use the appropriate commands for your system. You can also configure your browser to unzip and un-tar automatically as explained above for playing mpegs.
More info & free software: http://www.gnu.org/software/gzip/gzip.html
http://www.gnu.org/software/tar/tar.html
About the animations'
colormapping (For most movies/images): The entire simulation
region is outlined with a box. Red, orange, and yellow indicate
positive values, with yellow representing the greatest intensities and
red representing values near zero. Blue and green indicate negative
values, with green representing the greatest intensities and blue
representing values near zero. In some simulations, the most negative
value is mapped to yellow, so a yellow spot in the middle of green
represents the most negative point. |
 |
This TEM pulse (on a parallel-plate guide) starts out as positive, but after striking a PEC termination is reflected back negative.
Autoscaling vs. global
scaling: Two
kinds of color scaling are used. Autoscaling every
timestep scales the field intensities in that timestep to the full
range of color values. This means that dim timesteps will look as
bright as intense ones, but the structure of the fields in the dim
timesteps will show well. Autoscaling is used for each animation unless
global scaling is specified for that animation. Global
scaling over all timesteps scales the entire simulation
as a whole. Dim timesteps will barely show anything visible, but you
get a good idea of intensity variation over time.The following images demonstrate: both are taken from the same timestep of the same simulation:
|
 |
The image on the left is autoscaled to the values present in that timestep. The image on the right is globally scaled to the range of values for the whole simulation. Since the greatest intensities were present early in the simulation when a pulse stimulus was introduced, the image on the right is faint by comparison after the pulse has been smeared or stretched out by the transfer characteristic of the guide.
