Specifications

84 | august 2008 www.linuxjournal.com
INDEPTH
particularly the motion path of the different points. If you
can’t see any drift, you’re golden—you can skip ahead to the
export step. If the track is lacking, there are a number of ways
to tweak it. You can refine by adjusting the tracking algo-
rithms in the View→Controls menu, and rerun the track,
selecting refine instead of discard in the dialog that presents
itself to augment the track you’ve already created. You can do
much the same through adjusting the camera settings,
although if you do this, you’ll be better off running the track
from scratch.
A number of other refinement tools are also available.
You can pull up the modeling box (View→Modeling Tools)
and use it to add track masks and 3-D primitives to help
you spot drift, and it (along with the Fpoint track editor)
lets you delete, change or add new track points manually,
so you can direct the tracker to watch the right things and
make it ignore the wrong ones, such as people or cars in
the foreground. Once done, run the track again, again
selecting refine rather than discard.
You can watch the reconstructed camera motion, and
manipulate it to a certain extent, in the 3-D viewer window,
available through the View menu.
When you have a track you find satisfactory, go to File→Save,
and pick your export format. Be sure to export all the Fpoints—
having them helps if you’re going to need to do any complex
interaction, as they will help you guide where you put alpha
masks and such—like if you chose to do some of your
masking in your 3-D program.
Sticking In the Pins
In Blender, importing your track data will give you something
like what is shown in Figure 3.
The point cloud is a representation in 3-D space of the
track points from Voodoo, and the camera has applied to
it all the animation data (pitch, yaw, roll, position and lens
length) to re-create the movement that the original camera
engaged in. It is possible that upon import you will need
to re-orient parts of your scene, but if you’ve done your
job properly, all that needs to be done now is to finish
your 3-D UFO (texturing, animation and so on), and create
your dust cloud with your particle engine. Marrying these
elements together with the tracked footage is a job for
your compositor—Blender has a quite capable one built
in, which I covered in depth in the October 2007 issue
of Linux Journal.
With a bit of practice, you’ll have your own fake UFO
video suitable for posting on YouTube or fooling media
pundits. Like anything, camera tracking takes practice to
get right, but the toolset provided by Voodoo puts this
technique well within the reach of any hobbyists willing to
learn a bit about optics and spend some time training their
eyes. Refer often to the on-line help—Voodoo is one of
those rare freeware products with excellent documentation
built right in.
Until an open-source camera tracker of equal sophisti-
cation presents itself, Voodoo likely will remain the only
free camera tracker for Linux—at least in a price range
that end users can afford. All hail the grad students and
their advisors at the University of Hannover, Germany.
Let’s hope their excellent work remains free to use for the
foreseeable future!
I
Dan Sawyer is the founder of ArtisticWhispers Productions (www.artisticwhispers.com), a small
audio/video studio in the San Francisco Bay Area. He has been an enthusiastic advocate for free
and open-source software since the late 1990s, when he founded the Blenderwars filmmaking
community (www.blenderwars.com). He currently is the host of “The Polyschizmatic Reprobates
Hour”, a cultural commentary podcast, and “Sculpting God”, a science-fiction anthology podcast.
Author contact information is available at www.jdsawyer.net.
Figure 4. Finished Shot
Figure 3. Blender File with Voodoo Track Imported and Point Cloud Showing
For the savings, you do sacrifice
some sophistication in the ability to
fine-tune your shot, but for most
applications, Voodoo does very well.