Science SPORE Prize
November 2011

The Open Source Physics Project is supported by NSF DUE-0442581.

## User Comments on Tracker Video Analysis and Modeling Tool (9)

### How acceleration is calculated by tracker

Author: Eran Grinvald
Posted: October 27, 2014 at 5:33AM

I'm a physics teacher in highschool Israel and a part time researcher in the Weizmann Institure of Science. I'm new to tracker and think it is a fantastic tool and very excited about it.

I have two students which are frustrated that they can't reproduce the estimated acceleration calculated in tracker from the raw data (x,y,t) themselves, while they reproduce perfectly the velocities. I tried several algorithims I could think of to calculate the acceleration, all give quite different results, which means that for the specific object we tracked the time interval of the video is not short enough for numerical convergence. Yet non of the algorithims I tried did not reproduce the tracker result.

I could not find anywhere how tracker calculates the x (y) acceleration at a specific time, this without looking at the code itself.

Can anybody tell me what is the formula to calculate the acelleration in the x direction of point N (The first point that tracker calculates for is N=3, as a function of the data set x(i) and t(i) I think the standard algorithim for numerical second order integration can calculate for N=2 as well.)

Eran

### Re: How acceleration is calculated by tracker

Author: Wolfgang
Posted: Feb 09, 2017 at 3:20PM

> On Oct 27, 2014, Eran Grinvald posted:
>
> I'm a physics
> teacher in highschool Israel and a part time researcher
> in the Weizmann Institure of Science. I'm new to tracker
> and think it is a fantastic tool and very excited
>
> I have two students which are frustrated
> that they can't reproduce the estimated acceleration
> calculated in tracker from the raw data (x,y,t) themselves,
> while they reproduce perfectly the velocities. I tried
> several algorithims I could think of to calculate
> the acceleration, all give quite different results,
> which means that for the specific object we tracked
> the time interval of the video is not short enough
> for numerical convergence. Yet non of the algorithims
> I tried did not reproduce the tracker result.
>
> I could
> not find anywhere how tracker calculates the x (y)
> acceleration at a specific time, this without looking
> at the code itself.
>
> Can anybody tell me what is the
> formula to calculate the acelleration in the x direction
> of point N (The first point that tracker calculates
> for is N=3, as a function of the data set x(i) and
> t(i) I think the standard algorithim for numerical
> second order integration can calculate for N=2 as well.
>
>
>
> Eran

### Re: How acceleration is calculated by tracker

Author: Wolfgang
Posted: Feb 09, 2017 at 3:22PM

### What is the accuracy of position extraction by Tracker?

Author: Yang Zhou
Posted: April 21, 2018 at 6:33AM

To whom it may concern,
I intend to use Tracker to analyse the pedestrians crossing process on crosswalks.  I have some questions after I had import the video into the software.
1? What is the accuracy of position extraction by Tracker?
2?Can the software Tracker extract the position in small interval, such as 0.01s,0.05s?
3?The video is not recorded right above the crosswalk but in the oblique direction, is there any problems when extracting the trajectory?

### Re: What is the accuracy of position extraction by Tracker?

Author: Edwin Remolina
Posted: Aug 03, 2018 at 1:04PM

> On Apr 21, 2018, Yang Zhou posted:
>
> To whom it may
> concern,
> I intend to use Tracker to analyse the pedestrians
> crossing process on crosswalks.  I have some questions
> after I had import the video into the software.
> 1?
> What is the accuracy of position extraction by Tracker
>
> 2?Can the software Tracker extract the position in
> small interval, such as 0.01s,0.05s?
> 3?The video is
> not recorded right above the crosswalk but in the
> oblique direction, is there any problems when extracting
> the trajectory?
> Thank you for your help

Yang cordial saludo.

Me interesa mucho la investigación que está usted realizando. Por el momento con respecto a la precisión del software, yo estoy realización una investigación de correlación entre Tracker, el acelerómetro de los celulares y el acelerómetro de precisión Vericom 4000, precisamente para determinar la precisión y dar aplicación en la investigación de accidentes de tráfico.

Durante este semestre terminaré la investigación y estaré enviando información al respecto.

### Tracker for mac- Sierra

Author: Sonia Castro
Posted: September 3, 2018 at 4:47PM

Hello,
I would like to know if the last version of tracker works in mac-Sierra, since in the website only appears for mac OS

Thanks

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