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data—camera settings and movement, as well as the

“point cloud”—to various 3-D programs, and it is in the

3-D program where the magic happens. The 3-D program

also gives an extra measure of control and refinement

beyond what the tracker itself allows, as you can tweak

the camera animation curves.

I said earlier that the 1990s saw a lot of funding into creat-

ing software like this. Well, as every tech-junkie knows, where

thy research funding is, there thy grad students also will be.

Thanks to a team of particularly dedicated grad students in

Hannover, Germany, the technology to match camera move-

ment in three dimensions is available to Linux and Windows

users for free—a very good deal, considering that comparable

commercial packages run upward of several thousand dollars a

seat. For the savings, you do sacrifice some sophistication in

the ability to fine-tune your shot, but for most applications,

Voodoo does very well.

So, grab a copy of it, and let’s get you ready for your

appearance on the Art Bell show, peddling your newest

Genuine UFO Video (tm)!

The Incantation

First, head over to www.digilab.uni-hannover.de/

download.html, and download a package appropriate to

your system. Note that there are no source packages—

Voodoo may be freeware, but it is not, and probably never

will be, open source. So, grab the binary that is convenient

for you. Note that there are no x86_64 binaries available.

If you have a 64-bit system, just grab the x86 package—it

doesn’t depend on any 32-bit libs to work, and it won’t

choke on execution.

Pop open a command window, and use

tar -xvzf

open the archive. Next, move into the resulting voodoo-

versionnumber directory, then a further level deep into the /bin

directory, and run

./voodoo

The Bloodletting

Anyone familiar with old Roger Corman movies will realize

that bloodletting is an essential step in working good voodoo.

In this case, it’s your video that needs to be bashed into tiny

bits. Voodoo will not chew through video, it works only on

still image sequences.

A quick ffmpeg call will give you the image sequence

you require:

ffmpeg -i videofilename.avi -f image2 %03d.png

Once done, run Voodoo.

The interface, at first glance, is simple—two pull-down

menus and a flipbook player. That simplicity proves quite illu-

sory as you begin to delve into it. Camera tracking is complex,

and the toolbox here is extensive, but the nature of the task

means that you can learn gradually, and very little work will

get you a good initial track.

To start, go to the File menu and select load→image

sequence, and load up the image sequence you just creat-

ed. Be sure to set movement type and interlace settings,

or your track will not come out properly. Play the clip

through once with the flipbook to make sure there aren’t

any obvious errors.

Now, you need to load camera settings (File→load→initial

camera). This is vital if you want the track to work properly,

but it’s also very difficult to get right if you weren’t keeping

notes on the set for focal length, aspect ratio, film back and

(less important) skew angles. If you didn’t keep proper notes,

enter your best guess and go from there, you always can

tweak it later.

The work flow from here is pretty simple. Play through

the clip to make sure the whole sequence loaded properly,

then press track. The computer will select a few dozen

track points and follow them through the duration of the

clip. Depending on the complexity and length of the clip,

this process can run anywhere from a few seconds to a

few hours.

Once the track is done, play it through again, watching

INDEPTH

Figure 1. Voodoo Interface

Figure 2. Camera Settings Window

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Cradlepoint Escape Spécifications Page 84

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