Searching an option for calculating mean velocity for every Interrogation Area

[Andreas Müller]

I'm really pleased that I found your software in order to use it for  large scale-PIV in my lab experiments in the frame of my PhD-project. Thank you very much for creating this easy to handle application!

However I have one question left: Is there an option available to calculate the mean velocity (or any other of the display parameters) in every interrogation area for a certain number of frames ? I'm searching a similar option as the button "Calculate mean vectors" which is available under "Plot"-"Derive Parameters/modify data" (see the screenshot which I attached)..

In the changelog I saw the following entry:

22 Nov 2010

1.7.0.0

PIVlab 1.11: fixed a bug with incorrect results for line/ circle/ area extractions when a ROI was applied. Added a feature to calculate mean velocities of the whole session.

However I'm not able to find a function that can do it. Could you please give me a hint how compute parameters other than the vector arrows with PIVlab? It's probably very easy but at the moment I just don't get it.

With best regards

Andreas Müller

[William Thielicke]

Moin Andreas,
The option in the picture you showed is for calculating the average over time, keeping the data spatially resolved.
Do you want to calculate the average of an area?
Then you will have to go to "Extract data from area", then "Area mean value".

Does that help?

[William Thielicke]

Maybe I didn't get you right. If you want to calculate e. g. the mean vorticity, then you need to calculate the average velocity of all frames first by clicking on the button that you showed. Then select "vorticity" in the top most drop down menu and PIVlab will do that operation on the averga Velocity of the session.

[Andreas Müller]

Hello William,

your second post was exactly the answer I needed. I was a bit confused by the term " Calculate mean vectors" on the buttons, which I thought was just for the vector arrows. Now that I now I can also calculate the other parameters in a "mean of frames"-frames everything is fine! Thank you very much for the clarification!

I have a second question: For my experiments I want to do for example 3 different measurements. In the end I want to achieve one averaged velocity distribution. At first I thought that I will do the PIV analysis for every measurement and then export the results in order to calculate the average distribution in EXCEL. However then it will be tricky to import them again in PIVlab.

If I will use all the images at once in PIVlab, I will get false vectors at the "breakpoints" between the different measurements (meaning for example between the last picture of measurement 1 and the first picture of measurement 2). 

Is there any other possibility how to do this?

[William Thielicke]

Hi, if you select A-B, B-C,... then there should not be any problem.
If you want to have A-B, B-C,... Then you will need to duplicate the last image of the first measurement.
Difficult to explain, but in practice this is a very simple thing...