# Recalculating velocity with new frame interval

Tags: #<Tag:0x00007fa306c68b48>

#1

Hello! I’ve been manually tracking some data but realized that the frame interval I put in initially was incorrect. I’ve already manually tracked quite a few cells. How can I make the output velocity reflect a new frame interval after I’ve already tracked my cells?

Thanks!

#2

Velocity is just in um per time unit, you just need to reconvert to um per frame, then you can remultiply ratio them.

Example:
velocity = 25um/s with a frame interval of 2 frames per second
new (real) interval = 7 frames per second

$$\begin{split} \mathrm{new\ velocity} & = \mathrm{velocity}\times\frac{\mathrm{new\ fps}}{\mathrm{old\ fps}} \\ & = 25\mathrm{\mu m.s^{-1}} \times \frac{7\mathrm{\ frames.s^{-1}}}{2\mathrm{\ frames.s^{-1}}} \\ & = 87.5 \mathrm{\mu m.s^{-1}} \end{split}$$

#3

Thanks for the reply! But, is there any way to do this in imagej instead of manually as you suggest? I feel like it should be an easy fix to just change the interval and have the data update.

#4

Everything is usually one script away and usually easy if you know how to script and where to start.

But if you want some help and for someone to give his time, please provide the kind of data you are working on, as we cannot infer what manual tracking tool you are using or the format of your data from your initial post.

Best

#5

Thanks again oburri! Sorry, I’m still quite new to trackmate and the forum. Unfortunately, the forum isn’t allowing me to update documents because I’m a new user but the go-to sample that track mate provides should work fine as an example-- I’m manually tracking cells within 2-D images (200 stacks) through trackmate.

The default interval is 1 second for “tracks for trackmate”. Say, I were to manually track one of the particles and then decide I wanted to change my interval after I had done so by editing the image properties. Is there any way to update the analysis in track statistics to reflect a change in the image properties after I’ve already tracked my particles? Not sure if I’m phrasing my question correctly…

tldr: is there any way to update the track statistics window to reflect new image properties after manually tracking in track mate?