[Tutor] How to count vehicle? I'm trying but my code don't increasing..

[Steven D'Aprano]

On Tue, Sep 02, 2014 at 01:15:59AM +0700, Whees Northbee wrote:
> There's no vehicle in my code, my video just contain vehicles so I think I
> don't need to use haar classifier, so I'm just do background subtraction to
> get foreground which is vehicle movement because there's no other movement
> except vehicle and maybe little movement from trees...

Do you realise that this is a list for learning Python? We're not 
experts on video analysis. Probably nobody here except you has even the 
faintest idea what a Haar classifier is or whether you need one or not.

> I just use opencv module, like to do background subtraction..
> No, the code don't have any error.

If the code doesn't have any errors, then it must be working correctly. 


> The code is working smoothly to detecting vehicle and make rectangle of
> vehicle, 

How do you know? What part of your code shows you that it is correctly 
detecting vehicles?


> and I find center point of rectangle at (cx,cy)..
> I draw manually a line in video at coordinate (20,170) to (320,170)..
> When each of the rectangle vehicle cross or intersect with that line, I
> want to count it as 1..
> I already try:
> 
> *)I think, since the line is in the same y coordinate, so if the center
> (cx,cy),      cy=line y coordinate, the count increase
> 
>       if cy==170:
>           counter=counter+1
> 
> it doesn't work, no error but the counter stuck at 0

How fast are the vehicles moving? What is the resolution of the 
measurements? 


> Second try:
> *)I try to find distance between (cx,cy) and that line, if the distance is
> 0, counter increase
> 
>      dy=cy-170   #170 is y coordinate of line
>      if dy==0:
>           if (cx<=320) and (cx>=70):
>                   counter=counter+1
> 
> don't have error, but the counter sometime add sometime no..

Earlier, you said that it never worked. Now you say it sometimes works. 
Which is correct?

There is no difference between:

cy == 170

and

(cy - 170) == 0

So the question is, how do you know that cy ever equals 170?

Suppose the vehicle is moving towards the line. In the first frame, cy = 
300. In the second frame, 250. In the third frame, 200. Then, 150, 100, 
50 and then it's no longer in the picture. There is never a time that cy 
== 170. The logic of your code is wrong. You need to think of a 
different way to solve this problem.

Or, I could be completely wrong. I don't know, because I don't 
understand how this video processing works. I am just guessing.



-- 
Steven