Warning : Problematic image data, interpass-validation discarded 38% of the vectors in pass

[김민수]

Hello, I am a college student studying PIV in Korea. I'm contacting you because I encountered an error while analyzing Piv and couldn't find a solution.

The error I found is shown in the picture.

My questions are as follows
1. why are vectors being discarded due to interpass validation?
2. what is the impact of these errors on the interpretation?
3. How can I resolve these errors?

thank you for reading.

[William Thielicke (Shrediquette)]

Hi, this means that a large number of displacement estimates have been discarded after the first pass validation: the validation is based on the standard deviation, and local fluctuations in the displacement estimates. PIVlab assumes a more or less smooth velocity field in the images. If the velocity field has a too large standard deviation, then vectors are removed and filled with interpolated data. Piblab then hopes to find better velocity estimates in the following pass.

You could just run a single pass to see how your velocity field looks like. I bet it doesn't look too smooth.

Most likely, your image data is not really suitable for performing PIV analyses.

[김민수]

Thank you for your kind reply.

I actually analyzed it using pass1 and it wasn't smooth at all.

Do you have any suggestions on how to make it suitable for the image data? Do I need to post-process it?

2023년 10월 14일 토요일 오후 7시 26분 17초 UTC+9에 tras...@gmx.com님이 작성:

[William Thielicke (Shrediquette)]

I have no idea how the data looks like, so I cant give any advice. But post-processing will most likely not solve this. In most cases, the displacement or the noise is too high for proper PIV.