How to change units of a value?

I have data in data.speed which graphs in frames vs. pixels

I am trying to make it to show in seconds vs. cm

please help!!

it is 362 pixels in 5.7cm and 30 frames per second it is 360 seconds and 10800 frames the data is in a 10800 x 1 array

Answer 1

[dpb]

Gotta' know the frame rate and image resolution...if known, pretty simple to scale the axes; if not, "no way, no how"

"362 pixels in 5.7cm and 30 frames per second"

cmPer=5.7/362;  % cm/pixel conversion
secPer=1/30;    % sec/frame

t=secPer*[1:360*30];  % time vector in sec for t axis
v=cmPer*data.speed;   % speed in cm/sec
plot(t,v)

You don't need the temporaries simply to plot, of course, but if want to keep the normalized data...

[np]

it says error: vectors must be same lengths

[dpb]

Well, something ain't what you said it is, then...

>> 360*30
ans =
     10800
>>

ergo, the vector 1:30*360 is going to be length 10800 and you said that was what your data.speed vector is. Other than that, you'll have to debug; I can't see your terminal and don't have the data.

What does

whos t v

return?

[np]

My array was a little different a data was missing so it was 10799x1! it works thank you!!!

[dpb]

No problem--Knew it had to be something of the sort...

[Haziq Hakim]

Hi, I have a graph as follows:

Y Axis: Speed (m/s)

X Axis: Frames

How do i convert from Frames to Time(s) for the X Axis? My frame interval is 150ms, hence I am assuming there are 6.66 frames every second (1/150ms). There are a total of 465 frames.

Any pointers is much appreciated. Thanks in advance :)

[dpb]

Well, you're almost there...

interval=150/1000;  % 150 msec interval
N=numel(speed);     % number samples --> length of speed array
t=0:interval:(N-1)*interval;    % time vector to match

[Haziq Hakim]

Apologies for the late reply. Thank you so much! This helped a lot :)