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[deadmeatwalking]

i lol'd

Bringing girls to climax since 1969

[Scunner]

Drive Carefully?

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[Easymeat56k]

[Easymeat56k]

[Easymeat56k]

Bill, the early years.


Chester E. Macduffee next to his newly patented, 250 kilo diving suit, 1911.

[Scunner]

Reading the reviews of The Last Of Us, getting my hype on.

[EnjoyTheSauce]

Gawd damn ps3 exclusive.

[bigROBOTbill]

^^ wonderful photo Easy!!

[Easymeat56k]

I found "that" cat...

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[Mayhem_Lee]

I found "that" cat...

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Nice, I am reading those books currently.

[Easymeat56k]

[Easymeat56k]

[Easymeat56k]

[Easymeat56k]

[Easymeat56k]

A 1938 Phantom Corsair

[mycoolcar]

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I lol'd. Does this make me a bad person?

[Bounty Hunter]

The aforementioned rotor blade pictures (almost 2 weeks ago I know) is called aliasing in engineering terms.

It is when a continuous signal is sampled in discrete time steps, the information between time steps is lost and the resulting discretised signal is not a true representation of the original analogue signal.

This problem can be overcome by sampling above the Nyquist rate. The Nyquist rate is defined as being twice the bandwidth of the analogue signal, however sampling at 8 or 10, sometimes even 20 times the bandwidth of the analogue signal is usually required. There are techniques not discussed here which allow one to sample at less than the Nyquist Rate.

As can be seen in the spectrum of a sampled frequency, there exists 3 cases, where S (the Nyquist rate) is less than the bandwidth of the signal we get an overlap, which will lead to an incorrect representation, the other 2 cases are where S is high enough, thus there are no problems (except if it's too high, then you're needlessly reducing processor time - silly)


In the helicopter case either the frame rate or the shutter speed (refresh rate if digital CMOS) or both is synchronised with the frequency of the rotor blades, which like the image below leads to an incorrect representation of the analogue signal!

Here is a random image of a sinusoidal wave being sampled below the nyquist rate and the resulting discretised sinusoid.



Lets say the rotor blade of the helicopter are spinning at (fucked if I know) 500Hz? it honestly doesn't matter.

therefore the position of the blade at any given time t is:

y(t) = sin(f*2*pi*t)
y(t) = sin(1000*pi*t)

and if we sample this at say 500Hz (keeping in mind the Nyquist rate for sampling our helicopter should be at least 1000Hz) we get.....fuck it I'm not drawing it.

We get a line, on a line, with a magnitude of 1 at a frequency of 500 and another line, aliased down to a frequency of 0, which is also known as DC, or no frequency.

We sample up to 250Hz, (because the bandwith in discrete time is 0.5 which is equal to the analogue frequency over the sampled frequency) and 0.5 * 500 = 250Hz

and we get a magnitude of 1 at 0 Hz so our new discretised function becomes:

y'(t) = sin(0*2*pi*t)

and sin(0) = 0

this implies that for all times t, y'(t) = 0 in other words, the position of the rotor blades does not change.

AND THIS IS THE SAME SHIT AS WHAT'S HAPPENING HERE TOO!



fuck he's unstoppable!

[Scunner]

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[O-L-W-A-G]

http://en.wikipedia.org/wiki/Trigonometric_functions
http://en.wikipedia.org/wiki/Differentiation_(mathematics)

[PrinceTuiTeka]

Right, that's enough out of you BH, back in your box.

[Bounty Hunter]

This is real space porn.

[swindle]

I feel so dumb

EDIT: I am dumb.

[Retardobot]

I feel so dumb

EDIT: I am dumb.

Nah, you're just a different kind of smart.

[Bounty Hunter]

I feel so dumb

EDIT: I am dumb.

To be honest, given the same length of time, most people here would pick up these concepts fairly easily, it's just an investment in time, and a drive to sit and learn.

In the same length of time one could have learned a 2nd language, or learned how to cook.

Real intelligence comes in the form of using the knowledge.

[Easymeat56k]

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