On Tue, Sep 09, 2014 at 12:01:59AM +0100, Bruno Postle wrote:
> On Mon 08-Sep-2014 at 02:08 -0400, William Sherman wrote:
> >I then ran the "2. Align" step. And this took over 6 hours to
> >process. It was not fun waiting for that, and I dread what will
> >happen when I get to my "large" image collections! I did notice
> >that at times all the CPUs were going, and then other times just a
> >single CPU. Also, I'd be interested to know exactly what
> >"Optimizing Variables" were being optimized to get a sense for
> >where it is in the process.
William,
The optimization process cannot optimize a variable at a time: they
are all interconnected.
The optimization works a bit as follows. Suppose we have a function
that we don't know. In fact it's y=x^2, but again, we don't know that.
Suppose we want the result to be "10". So we try puttin in "1" and get
"1" put in "2" and we get "4". From this we calculate that adding one
to x, results in "3" more in the output. We need 6 more output, so we
add 6/3 = 2 to the input. 2+2 = 4, so we try 4 next. We get "16",
which is way too far. now we have from 2 to 4 on the input the
difference in output is 12, and we need to be exactly in the
middle. So we probe exactly in the middle: 3. So now we get "9" and
need to go a little higher. 16-9 is 7, we need to be 1/7th on the way
from 9 to 16, 1/7th of the way from 3 to 4: 3+1/7 = 3.1428. Now we get
pretty close, and it gets annoying doing this by hand. But now that we
are close, we get closer really, really quickly. Just a few more steps
and we'd have our solution to many decimal places. (after these few
steps "by hand, we have only a 0.6% difference with the mathematical
solution).
For panoramas there are a whole lot of parameters to adjust. This
means that there no longer is a "mathematical solution". But the
"approximation technique" still works. So for hugin to optimize the
panorama, it calculates how much to change all the parameters at once,
then it changes them all and next it will start the process of finding
how much to change each one all over again.
>From my example, you can see that if you start off with a "pretty bad"
estimate, it takes a few iterations to get close enough to get into
the "gets closer really really quickly" region. The number of
iterations required to get "close enough" gets more and more as the
number of parameters increases.
Roger.
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