Re: [BLACKBOX] Another LibVector question

From: [at]} <Wojtek>
Date: Fri, 27 Mar 2009 20:41:10 -0400

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It is truly confusing. The correlator adds its latency to the correlated
waveform. The latency is equal to 1/2 the FIR length. But the Conv
function adds the correlator length to the correlated wave.

All the indices are now mismatched with respect to the original
feature in the ADC waveform.

Now I have an explanation how it was possible that some brave French
pilot flew unnoticed all the way over Soviet Union and landed
on the Red Square. As we all know, Russians love BlackBox.
They must have used Lib to write radar pattern recognition.
But they got confused with the LibVector indices just like myself.
The pattern recognition missed the peak in the correlated radar
data and no alarm was sounded.

The most important goal when dealing with the enemy is to get
the enemy thoroughly confused. I am not looking at my waveform
processing and I can appreciate how it was achieved.

W.

On Fri, 27 Mar 2009, Wojtek Skulski wrote:

> Robert:
>
> here is another question concerning LibVectors.Conv.
>
> This procedure extends the original data and returns
> a vector whose length is a sum of A+B, where A and B are vectors
> being convolved. It seems extremely cumbersome to me.
> Now I have to relate the index of a pattern found
> in the convolved vector with the one in the original
> vector.
>
> As you know one of main applications of the convolution
> is finding patterns. (Well, in this case the convolution
> is called "correlation", but I am a practical person,
> so I am not splitting the hair over those names).
>
> Now I found the pattern by looking at maximum of the
> correlation, but the maximum is shifted with respect
> to original data. It is confusing at best.
>
> Any comments why it should be so?
>
> IGOR is quietly extending the data in order to provide
> the "warmup region" for the FIR, but then it discards the
> extended pieces before returning the correlation result
> to the user.
>
> I know you will not change LibVectors after they are out
> for so many years.... but it is confusing to find those warmup
> regions in the result...
>
> W.
>
>
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Received on Sat Mar 28 2009 - 01:41:10 UTC