how to plot streamline

I have the 2-D PIV data like below and I am not able to get streamlines in matlab:

ix,iy,iz = image coordinate X,Y,Z [pixel]

dx = displacement component X [pixel] * (image resoltion) = mm

dy = displacement component Y [pixel] * (image resoltion) = mm

--------------------------------------------------

So I have dx and dy in mm. Also I can calculate: du = dx/dt , dv = dy/dt as the velocities in x and y directions.

I want to get the streamline usnig streamline/streamslice functions in matlab but I do not know how to define startx and starty?? Should I use meshgrid function for that? and shoul I use ix,iy(image coordinates) OR dx,dy to define startx and starty points?

Moreover do I need to define meshgrid for du,dv to fill velocities for every point??

Any help would be appreciated.

A = xlsread(......myfile.xls);  % myfile.xls contains all data.
dx = A(1:end,4); % size(dx) = 8400*1
dy = A(1:end,5); % size(dy) = 8400*1
du = A(1:end,6); % size(du) = 8400*1
dv = A(1:end,7); % size(dv) = 8400*1

[startx,starty] = ?????
[X,Y] = meshgrid(dx,dy);
streamline(X,Y,du,dy,startx,starty); 
    

[Ham Man]

The streamline/streamslice gave me an error stating that U,V should be 3D data. How can I make those in 3D?

Answer 1

[KSSV]

Try:

skip = 2 ;                  % can be changed 
startx = X(1:skip:end,1:skip:end) ; 
starty = Y(1:skip:end,1:skip:end) ; 
streamline(X,Y,du,dy,startx,starty); 

Also have a look on streamslice. This would be a better function to use.

[Ham Man]

Thanks for replying KSSV.

It gave me an error for the size of du and dv. Shouldn't be du and dv in the same size of X,Y? X and Y are now a grid but du,dv are both have one column.

size(X) = size(Y) = 8400*8400

size(du) = size(dv) = 8400*1

[Ham Man]

Is this true for input argument for "streamline" function:

streamline(x displacement,y displacement,velocity in x direction,velocity in y direction)??

[KSSV]

(x,y) are locations at which you have velocitties (u,v). If you don't have locations you can plot w.r.t indices.

[Ham Man]

The streamline/streamslice gave me an error stating that U,V should be 3D data. How can I make those in 3D?

[KSSV]

Share your data.

[Ham Man]

Here is my data. Thanks for your attempt.

ERROR:

Error using streamslice (line 142)

Volume data arguments must be 3-D arrays.

[Ham Man]

I wonder how to make du,dv in the same size of X,Y? should I use reshape or repmat to make du and dv in the same size of X,Y( made by meshgrid(dx,dy) )?

otherwise the streamline are not achievable.

[KSSV]

T = readtable('https://in.mathworks.com/matlabcentral/answers/uploaded_files/687023/ane1_data.xlsx.xlsx') ;
T(8447,:) =[] ; % remove NaNs 
x = T.(1) ; y = T.(2) ; 
dx = T.(4) ; dy = T.(5) ; 

[X,Y] = meshgrid(linspace(min(x),max(x)),linspace(min(y),max(y))) ; 
dX = griddata(x,y,dx,X,Y) ; 
dY = griddata(x,y,dy,X,Y) ; 

streamslice(X,Y,dX,dY)

[Ham Man]

Awesome, Many thank to you. This is what I was looking for. Much appreciate.

I tried "streamline" function but no luck. How does it work with these data?

[KSSV]

T = readtable('https://in.mathworks.com/matlabcentral/answers/uploaded_files/687023/ane1_data.xlsx.xlsx') ;
T(8447,:) =[] ; % remove NaNs 
x = T.(1) ; y = T.(2) ; 
dx = T.(4) ; dy = T.(5) ; 

[X,Y] = meshgrid(linspace(min(x),max(x)),linspace(min(y),max(y))) ; 
dX = griddata(x,y,dx,X,Y) ; 
dY = griddata(x,y,dy,X,Y) ; 

streamline(X,Y,dX,dY,X,Y)

And thanks is accepting/ voting the answer.

[Ham Man]

Perfect. Thanks again KSSV.