VJ Night

There might have been about 20 people there to watch the show. Around 8 VJ Scobot started out with his opening set, which was mostly fast edits between a few dozen clips. Some of the clips were recognizable, like from Bad Boys or Team America, others from anime sources, and some footage from marginal productions of decades ago. Something from early incarnations of 'The Rocketeer'? Scobot later explained that his software allows keying of clips to keys (and presumably effects and transitions also?).

After 20-30 minutes of that the music wound down and Scobot introduced DJ Deeb, the guest VJ Spyscience, and what VJ Night is all about. An interview with Spyscience followed, video taped by one from the 911 crew (though it's not clear whether the interview will ever be put on the internet or anywhere else, it's just for the archive). Spyscience used some software I forget the name of, which is also clip oriented but drag and drop along with an external USB device with sliders and knobs is used. Most of the clips where provided with the software, one he had made himself. His computer locked up a few of times and Scobot had to take control of the video for a while during rebooting.

After that a Q&A sessions followed, and the event was over by about 10.

Overall the event was interesting, though even as Scobot admitted the traditional role of VJ work is to make a side-show, not to be shown in a theater to an audience focused directly on it. I thought the format works but that VJ sets should be a little shorter, since they can get repetitious. Another nice thing might be to have continuous split-screen, one view showing the VJ output and the other focusing on the VJ and what they're doing, although the layout of the space allows the audience to effectively look over the shoulder of the working VJ.

I found my personal preference is for visuals that are the opposite of recognizable clips from tv or movies, but purely abstract instead. I'd like to see someone do a set with more live-generated visuals (rather than live-editing-plus-effects on a lot of clips).

Gephex

I created a couple of custom gephex modules (for 0.4.3):

Average

Find the average color or brightness of a framebuffer. (maybe add HSV next)

Slow motion

Play back snippets of framebuffer input in slow motion. The music is from ccmixter, William Berry's Time To Take Out The Trash.

The source code (GPLed of course) and windows dlls are provided in those zip files.
More custom effects are on the way.



New video showing off basic gephex effects:




...but none of those I just created. Maybe next time.

Phoeeb Deform

Brand new video, made almost from scratch (a stock photograph from deviantart was used as a referenced and applied as a texture).





Phoeeb Deform from binarymillenium on Vimeo.




The music is from ccMixter (http://ccmixter.org/media/files/vincent_vega11/6966), which has supplied me with several good soundtracks for recent videos, although it can be difficult to browse the music- where's the sort by rating button? I recall another CC music site less focused on remixing and more on original works that had more movie like soundtracks I'd like to use in the future but I forget the site.

Deriving The Rocket Equation

This is probably a job interview question somewhere. I was just thinking about it
and decided to try it out myself, with no regard to convention beyond what is already intuitive for me.

The question is, you have rocket with a certain amount of mass, some of which is fuel. The rocket consumes fuel at a constant rate in order to produce a constant thrust. If the rocket starts at time zero, how fast is it going and what is its displacement at some later time?

So the lets say the fuel consumption rate is a positive number k, in units of kg/sec.
The fueled mass of the rocket is Mo.
Therefore the mass at a later time t is
M(t) = Mo - kt

From physics it is known that F=MA. Our F is constant, we'll just call it F, its units are kg*m/s^2. Acceleration is the thing that will change, intuitively acceleration should increase as the mass goes down as fuel is consume.

A= F/M = F/M(t) = F/(Mo - kt)

Looking at that equation makes sense- the denominator gets smaller therefore A goes up as time increases.




So the trick to finding velocity is integrating that curve and position is found by integrating again. Easy numerically, but of course we want a nice analytical answer.

I've forgotten a lot of the little tricks of calculus, which is just as well since I want to solve this as intuitively as possible anyway. The most I did lookup to remind myself was to find that the integral of 1/x is ln(x) and that ln(x/y) = ln(x) - ln(y), and that to have definite integral over a specified interval (time 0 to time t1 here) you can subtract the indefinite integral of the lower bound from the indefinite integral of the higher bound.

We don't have a 1/x equation, at first glance, we have a 1/(constant- x) equation- so how do you integrate that? The trick is to make our equation into the form of 1/x.

1/x backwards to our acceleration graph:

So we need to reverse our graph to make it look like that and then we'll have the integral. Instead integrating with respect to time, we'll integrate with respect to (Mo-kt) and do it from the lower bound Mo-ktf (tf is the final t) to Mo (Mo - k to, to is zero so it's just Mo).

So we end up with

Integral of F/(Mo-kt) d(Mo-kt) = F * Integral of 1/(Mo-kt) dkt
(since Mo does not change the interval d(Mo-kt), it drops out). Unfortunately the units of this integral is going to be kg*m/s^2 * 1/kg * kg/s * s (the units of the F times the units of the 1/ mass times the units of the k times the units of the t) = kg*m /s^2 - we want velocity not force! In order to cancel out the k in dkt inside the integral we divide F by k outside of the integral.

f/k units is m/s - a velocity which we should return to later.

f/k * ( ln(Mo) - ln (Mo - ktf) ) = f/k * ( ln (Mo/(Mo - ktf)) )

Or if we say Mf = Mo - ktf, then v(t) = f/k * ln(Mo/M(t)).

Exhaust Velocity

Going slight further in, we should look at what is happening in order to accelerate the rocket. Rockets operate by throwing mass out the back end at a high velocity- throwing out a little bit of mass a high velocity adds a little velocity to your rocket with a big mass- and there's an equation of momentum to show
how those four things are related:

m1 * deltaV1 = m2 * deltaV2

We know we're burning m1 = k amount of fuel every second, and that since we're not doing any nuclear reactions the k amount of fuel is still there in mass form- it's just moving out the back end at high velocity. We know the mass of the rocket Mo or M(t) and its acceleration (delta-v) for that moment is a(t). So we have three of the four quantities, the delta-v of the exhaust fuel is what we want. Since the exhaust velocity doesn' t change we can just use Mo = M(0) and a(0)*1 second = F/Mo*1second (to simplify we assume that acceleration doesn't change much over 1 second).

m2*deltaV2 / m1 = deltaV1
Mo*F/Mo* 1sec / ( k * 1sec ) = deltaV1
exhaust velocity deltaV1 = F/k - the same f/k in the above rocket equation. So instead of saying f/k we can say 'exhaust velocity'.

Gravity

Gravity from binarymillenium on Vimeo.