Who doesn't love Tracker Video for the analysis of videos? What isn't there to love? Free? Yes. Multiple platforms? Yes (Mac OS X, Windows, Linux). And now, perspective corrections (latest version is 4.05).
How many times have I looked at a video and had a problem with perspective? The simplest video to analyze is one with the camera far away from the object and looking perpendicular to the object's motion.
Here is an example video I made of a bouncing ball. Normally, I would set up the camera perpendicular to the ball's motion. In this case, I just put it anywhere. However, I did mark a 1-meter square box on the wall (in removable masking tape - trust me, it will come off).
Let me show you how to use Tracker Video and still plot the motion of this ball. Ok, I will admit that even this case isn't perfect (the camera is too close and the ball's motion is blurry).
First, load up your video. Then choose videos-Filters-New-Perspective. You will get this box that you can adjust. Here is that box with my adjustments.
Since this was a 1 meter x 1 meter box, I entered values for points 0 - 3 as (0,0), (0,1), (1,1), (1,0). Simple. Now do video analysis as usual. Oh, you can check your correction by clicking the "output" button. Here is what you get.
Awesome? Yes. Ok, now to the data. I followed the motion of the bouncing ball. Here is the y-position with a quadratic fit.
Here you can see that the fitting equation says the ball has a vertical acceleration of around 14 m/s2. Clearly, this isn't quite correct. Let me go ahead and show the horizontal motion.
Here you can perhaps see the problem. When the ball is closer to the camera, the error in the position of the ball gets exaggerated.
I am still pleased. This was just a trial. I suspect if I had the camera further away, the problem wouldn't be so bad. Still, a great feature of Tracker Video.
There is already a video that I have been holding onto for a REALLY long time that I am going to use this on.
