Accessing PIV Results

[abd...@columbia.edu]

Is there any documentation on where the results are stored in the most recent update? I was hoping to use PIV lab to pull results for further analysis of specific locations within an image. I'm looking at the resultslist.mat file as this seemed the likely location:

I found that resultslist is a M by N matrix where N is the number of timepoints. Each element in this is also a sub-matrix of the same size (m by n, for my example this was 49 by 52 --> presumably the matrix size for the velocity vectors).

I am GUESSING that the convention is the following:

• 1st row (M=1) of matrix  is x-position in pixels
• 2nd row (M=2) matrix is y-position in pixels
• 3rd row (M=3) is x-velocity (pixels/frame)
• 4th row (M=4) is y-velocity (pixels/frame)
• 5th row (M=5) = ? (this is filled with values of 1, I am not sure what this is
• 6th row (M=6) = empty
• 7th row (M=7) = ?
• 8th row (M=8) = ?
• 9th row (M= 9)= ? (filled with values of 0, 1,and 2)

Is someone able to explain the way this data is stored? Example picture attached for clarity.

[William Thielicke]

Hi, you an simply export the data as mat or ASCII or whatever file format, then it's much easier to process and understand.

[abd...@gmail.com]

I'm not sure I understand how this helps or is different from what I did:

I saved the session and looked at the PIV data files in matlab, so I was looking within a .mat file (resultslist.mat). Is this different from exporting the data as a mat? If so, can you give a pointer for how to do so? Thanks!

[William Thielicke]

Hi, saving sessions is only for reloading them in pivlab. If you want to export your data, then you need to save the data (file -> save)

[Alexei Sondergeld]

Is there a way to make it save the data when doing a batch run?

[William Thielicke (Shrediquette)]

Wich data? The session that you process in batch with the GUI are saved automatically after each processed session file.

[Alexei Sondergeld]

Some sort of data that is readable in Matlab without using the PIVLab app. If I open the session file (which is all it creates) in Matlab it just has lots of single-number variables plus a few file names and small matrices (which don't look big enough to be the actual vector fields or other data from the processing). I know it's possible to manually save the data with the GUI but I'd rather not do that one-by-one for 200+ analyses.

[William Thielicke (Shrediquette)]

Please check the mix example files, they contain all information you need.

[Alexei Sondergeld]

I'm not seeing a .mlx file anywhere in the PIVLab results, and I also searched the entire folder in Program Files that contains Matlab 2024a and there were no mlx files related to PIVlab. Essentially all I want to know is how to tell it to make the same plot out of the information that's somewhere in every one of the session mat files without having to manually hit "calculate average," navigate to the streamline file, make the streamlines, and then navigate through a ton more dialog boxes (same ones for every session file though) for 168 trials. This will likely take several days just to manually generate all of these plots. It would also be nice to be able to automatically save parameters from "extract from area" without having to manually press "export" on every one. Plus - if I ever have to do something even as simple as changing a line weight or color or something, that will require repeating these days of manual plot generation and saving. If that requires these mlx files, is there some kind of documentation on how to set this up for PIVLab? Or where the actual data/vector fields/etc. is stored in the session file, so I can bypass the GUI? 

[William]

Here are some screenshots showing how to navigate to the relevant mlx files. You can then edit them and do whatever you want to do automatically. But you will need to know how to write code in Matlab (and this isn't something I can offer):