Boundary tracking u,v vectors

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Leonidas Leonidas
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Boundary tracking u,v vectors

Hi all,

basically just getting started with the tool. I  used it a little in the past but I need something more specific this time.

Is it possible to extract the u,v vectors of the points of a boundary that is moving between two images with this tool?

I want to get the velocity of this boundary so that I can interpolate intermediate steps of the boundary's position that I don't have any experimental data.

Could someone suggest a way to succeed this?

Thank you,

Leo

Leonidas Leonidas
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Re: Boundary tracking u,v vectors

I guess one way is to extract the data in ASCII code and then check the pixel coordinates of where the desired boundary lies in the first image that I have imported. Then I should isolate only these points from the whole image...

Thank you myself.
If someone else has some other idea that could be done within the tool please let me know.

Leo
William William
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Re: Boundary tracking u,v vectors

Dear Leo, I think working with ASCII tables can't be the best solution for your problem. However, I have difficulties to understand what you want  to do. Maybe adding a drawing /picture would help.

Please consider donating for the PIVlab project:
http://paypal.me/pools/c/81Y8wBVi4y

The developer needs to update to a recent Matlab release in order to keep the project running.

William William
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Re: Boundary tracking u,v vectors

In reply to this post by Leonidas
Do you want to measure velocities that are not on a global cartesian grid, but on a grid that is fixed to a moving object?

Please consider donating for the PIVlab project:
http://paypal.me/pools/c/81Y8wBVi4y

The developer needs to update to a recent Matlab release in order to keep the project running.

Leonidas Leonidas
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Re: Boundary tracking u,v vectors

Hi William,

I think my case is quite simpler. It will be the cartesian grid or a pixel valued grid however we want to call it but I need only the velocity of the boundary which is moving and not the rest of the picture which is calculated along with it.
So I think extracting the velocity vectors for every pixel and keeping the information of those that my boundary overlaps with may work.

I haven't tested it yet but this will be my approach.
Thank you for your response, what are your thoughts on the working principle I described?

Thanks.
Leo

Στις Δευ, 24 Σεπ 2018 στις 12:19 μ.μ., ο/η William [via PIVlab - Time-Resolved Digital Particle Image Velocimetry Tool for MATLAB] <[hidden email]> έγραψε:
Do you want to measure velocities that are not on a global cartesian grid, but on a grid that is fixed to a moving object?

Please consider donating for the PIVlab project:
http://paypal.me/pools/c/81Y8wBVi4y

The developer needs to update to a recent Matlab release in order to keep the project running.




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Leonidas Asimakoulas 

PhD candidate at QUB

Low Temperature Plasma Laboratory

Centre for Plasma Physics (CPP)

School of Maths and Physics
BT7 1NN,
Northern Ireland, U.K.

Leonidas Leonidas
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Re: Boundary tracking u,v vectors

In reply to this post by William
Hi William,

Just imagine the case of a balloon expanding.
I am only interested in the velocity of the boundary of the balloon for my data.

It seems to me that there are other areas in my image that are calculated as well since the way the light falls on the balloon changes the value of the pixels. So I binarized the image to have a black balloon and a white surrounding area in order to calculate only the velocity of the boundary.

However the software will return the vectors for other pixels as well. So I believe if I take all the velocity vectors for every pixel coordinate and then keep only the calculated velocity for the overlapping pixels with this boundary may be a good approach.

I hope it is clearer now.
William William
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Re: Boundary tracking u,v vectors

Binarizing is often a problem for PIV analysis, as PIV is based on textures and a BW image does usually not have textures. If your background is not moving, then you can just eliminate all vectors below e.g. 0.01 m/s.

Please consider donating for the PIVlab project:
http://paypal.me/pools/c/81Y8wBVi4y

The developer needs to update to a recent Matlab release in order to keep the project running.