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Experiences with OpenCV

OpenCV has really lots of useful classes and features.
The square detection for my virtual reality class work is being made with it.

Unfortunately, on my tests, I was detecting squares which I didn't want the software to detect. Like on the image below:It would be much better if I could do the image analysis only inside the laptop screen. "Googling" on "OpenCV image crop" I had reached the (OpenCV Region of Interest - ROI). This blog has a good explanation on how to crop (extract the region of interest) from a image.
With those informations I got the following result for the same frame:

Now I have to check the area of the detected squares. At the web archives of the computer geometry class mailing list, from the Illinois University, google had shown me one algorithm to calculate the area of a closed polygon, as follows:
Let 'vertices' be an array of N pairs (x,y), indexed from 0
Let 'area' = 0.0
for i = 0 to N-1, do
Let j = (i+1) mod N
Let area = area + vertices[i].x * vertices[j].y
Let area = area - vertices[i].y * vertices[j].x
end for

In C, to use with OpenCV:
double polygonArea(CvPoint vertices[]){
double area = 0.0;
int i, j;
for (i=0;i<4;i++){
j = (i+1) % 4;
area = area + vertices[i].x * vertices[j].y;
area = area - vertices[i].y * vertices[j].x;
if (area<0) area = -area;
return area;


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uSleep on windows (win32)

I am facing a terrible issue regarding timing on windows.

Googling arround, I've found those infos:
Using QueryPerformanceCounter and QueryPerformanceFrequency APIs in Dev-C++
QueryPerformanceCounter() vs. GetTickCount()
How to time a block of code
And Results of some quick research on timing in Win32
With that I'm trying to write something like a uSleep function for windows:


voiduSleep(int waitTime){
__int64 time1 = 0, time2 = 0, sysFreq = 0;

QueryPerformanceCounter((LARGE_INTEGER *)&time1);
QueryPerformanceFrequency((LARGE_INTEGER *)&freq);
QueryPerformanceCounter((LARGE_INTEGER *)&time2);

// }while((((time2-time1)*1.0)/sysFreq)<waitTime);
}while( (time2-time1) <waitTime);

There is also already a nanosleep…

More trickery with gnuplot dumb terminal

In my post "Plotting memory usage on console" the chart doesn't pan the data.
Now, using a named pipe, the effect got a little bit nicer.
First, we have to run the script to get a file filled with memory usage info:
./ > memUsage.dat &
Then we have to create a named pipe:
mkfifo pipe
Now we have to run another process to tail only the last 64 lines from the memUsage.dat
while [ 1 ]; do tail -64 memUsage.dat> pipe; done &
And now we just have to plot the data from the pipe:
watch -n 1 'gnuplot -e "set terminal dumb;p \"pipe\" with lines"'
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Checking auth.log for ssh brute force attacks

As I am letting my personal computer always on, as a homelinux server, I decided to check if someone is trying to breaking in with SSH brute force attacks.

First I did a grep for fail at the /var/log/auth.log. (grep -i /var/log/auth.log)

And I got lots of lines with the string "fail". With [grep -i /var/log/auth.log | wc -l] I figured out that were 1164 fail entries at auth.log

With an [grep -i fail auth.log | cut -d " " -f 6 | sort | uniq] I checked that were two kind of failed attempts:

So I wrote the following line to check with which users they were attempting to log:
grep Failed auth.log | cut -d " " -f 11 | sort | uniq | while read line ; do echo -n $line" "; grep $line auth.log | wc -l; done | sort -n -k 2

Here, the field position (the number 11 at the above command lines [-f 11]) may change in some systems. At my desktop at work, the username came at the position 9.

Here are the "top ten":
root 2922
user 2884