Why won't my contour work?

So I have been able to generatae a contour plot for a full data set. For one of my experiemnts there are bad vectors that should be removed from said data set. I have modified my code as follows but I cannot get the contour plot to work. It says "Z must be at least a 2x2 matrix."

Can someone help me please?

function [x,y,u_avg,v_avg,CHC_tot] = piv_averages(prefix,suffix,Nstart,Nfinish,interp)

% This program reads in a series of instantaneous PIV vector fields from
% Insight and averages them.  The user has the option of excluding
% interpolated vectors, which have CHC > 1.  (interp = 0 means do not 
% interpolate, while interp = 1 means interpolate).

% Create file name for each image
c_exit=2.776; %speed of sound
x0=1040; %origin of the jet in pixels  
y0=53.8; %origin of the jetin pixels
D=923.71; %diameter of jet exit in pixels 
v_shift=0;
for i = Nstart:Nfinish
    Nstring = int2str(i);       % Convert iteration number to a character string
    if i < 10
        filename_inst = strcat(prefix,'0000',Nstring,suffix);
    elseif i < 100
        filename_inst = strcat(prefix,'000',Nstring,suffix);
    elseif i < 1000
        filename_inst = strcat(prefix,'00',Nstring,suffix);
    elseif i < 10000
        filename_inst = strcat(prefix,'0',Nstring,suffix);
    else
        filename_inst = strcat(prefix,Nstring,suffix);
    end

    % Read file name
    A_inst = csvread(filename_inst,1,0);

    x = A_inst(:,1)+0;             % x-position (mm)
    y = A_inst(:,2)-198.2;             % y-position (mm)
    u = A_inst(:,3);             % x-velocity (m/s)
    v = A_inst(:,4);             % y-velocity (m/s)
    chc = A_inst(:,5);           % number of good vectors at this location

    N = size(x,1);               % Length of entire vector array
    
    % Initialize output variables if this is the first file
    if i == Nstart
        u_tot = zeros(N,1);
        v_tot = zeros(N,1);
        CHC_tot = zeros(N,1);
    end
     
    for j = 1:N
        if interp == 0
            if chc(j,1) == 1
                u_tot(j,1) = u_tot(j,1) + u(j,1);
                v_tot(j,1) = v_tot(j,1) + v(j,1);
                CHC_tot(j,1) = CHC_tot(j,1) + 1;
            end
        elseif interp == 1
            if chc(j,1) > 0
                u_tot(j,1) = u_tot(j,1) + u(j,1);
                v_tot(j,1) = v_tot(j,1) + v(j,1);
                CHC_tot(j,1) = CHC_tot(j,1) + 1;
            end
        end
    end
end

for j = 1:N
    u_avg(j,1) = u_tot(j,1)/CHC_tot(j,1);
    v_avg(j,1) = v_tot(j,1)/CHC_tot(j,1);
end

% define orifice opening in pixels 
orificepl=linspace(0, x0-(D/2));
orificepr=linspace(x0+(D/2), 2016);
yorifice=2016*ones(size(orificepl));

% define orifice opening in mm
orificeml=linspace(0, (x0-(D/2))/48.11);
orificemr=linspace((x0+(D/2))/48.11, 2016/48.11);

% define orifice opening non-dimensional
orificendl=(orificepl-x0)/D;
orificendr=(orificepr-x0)/D;

% Set origin to jet exit centerline
x_c = x - (x0);
y_c = y - y0;

% Shift by convective velocity
v = v - v_shift;

% Nondimensionalize variables
x_non = x_c/D;          % Nondimensionalize using jet diameter
y_non = y_c/D;          % Nondimensionalize using jet diameter
u_non = u_avg/c_exit;       % Nondimensionalize using sonic speed
v_non = v_avg/c_exit;       % Nondimensionalize using sonic speed

% %%%%%%%FOR H/D=2%%%%%%%%%
% 1) Choose a threshold
yThreshold = 300; %accept all vectors that start at or above y = yThreshold; 
% 2) identify all quiver arrows that meet the criteria 
acceptIdx = y >= yThreshold; 
% 3) plot the quiver arrows, but only the ones accepted
% figure(5)
% quiver(x(acceptIdx), y(acceptIdx), u_avg(acceptIdx), v_avg(acceptIdx), 5)
% % add reference line at threshold if you'd like
% line(x(acceptIdx),yThreshold,'linewidth', 4, 'color', 'k'); 

aa=(yThreshold/2-67.8)*ones(size(acceptIdx));
aa_non=((yThreshold/2)-y0-67.8)/D*ones(size(acceptIdx));

x_non_d=downsample(x_non(acceptIdx),15);
y_non_d=downsample(y_non(acceptIdx),15);
u_non_d=downsample(u_non(acceptIdx),15);
v_non_d=downsample(v_non(acceptIdx),15);

%for contour 
N = size(x(acceptIdx),1);          % Length of entire vector array
xsize = 1;
x1 = x(acceptIdx(1));
x2 = x(acceptIdx(2));
while (x2 > x1)         % Calculate number of x-locations using while loop
    xsize = xsize + 1;
    x1 = x2;
    x2 = x(acceptIdx(xsize+1));
end

ysize = N/xsize;        % Calculate number of y-locations


% Parse x- and y- positions to avoid repetition
for i = 1:xsize
    x_re(i,1) = x_non(acceptIdx(i,1));
end
for i = 1:ysize
    y_re(i,1) = y_non(acceptIdx(1+(i-1)*xsize,1));
end

mag = sqrt((u_non(acceptIdx)).^2 + (v_non(acceptIdx)).^2); 

% Reorganize data for contour plots
mag_re=[reshape(mag,xsize,ysize)]';
u_re = [reshape(u_non(acceptIdx),xsize,ysize)]';
v_re = [reshape(v_non(acceptIdx),xsize,ysize)]';

%Contour Quiver
figure(7)
contourf(x_re,y_re,mag_re);
cb = colorbar(); 
colormap(jet)
ylabel(cb,'|U_P_i_s_t_o_n/U|')
hold on
qp=quiver(x_non_d,y_non_d,u_non_d,v_non_d,3,'k')
line(orificendl,yorifice/1008, 'linewidth', 4, 'color', 'k')
line(orificendr,yorifice/1008, 'linewidth', 4, 'color', 'k')
line(x_non,aa_non, 'linewidth', 3, 'color', 'k') %only for H/d=2
hold off
axis([-1 1 0 2])
xticks([-1 0 1])
yticks([0 1 2])
set(gca,'YtickLabel',2:-1:0)
set(gca,'XAxisLocation','top','YAxisLocation','left');
xlabel('z/D')
ylabel('x/D')
% title('Nondimensional velocity field')
set(findall(gcf,'-property','FontSize'),'FontSize',16)
end 

A link to my data set can be found here since it is too large to upload.

https://drive.google.com/open?id=1Lk1zYrgMKFVlWNVuELOkrU85PJ5HN7xF

Thank you in advance!

[Walter Roberson]

What input should be used in calling piv_averages() ?

The data you linked to is a .mat but the code needs a csv to read ?

[Monique Embury]

I am actually using a series of 100 image pairs taken using PIV. The file that I attached is the average of those 100 image pairs which are .vec files. Everything in my code works except for the contour plot. If AcceptIdx is removed it works fine.

[Walter Roberson]

Well that's nice, but I cannot test it without knowing the input values and having the input files. You have provided one variable in the .mat file, and I, as an outside observer, cannot assume the value of any of the variables.

By the way, you can make your code shorter. Replace

    Nstring = int2str(i);       % Convert iteration number to a character string
    if i < 10
        filename_inst = strcat(prefix,'0000',Nstring,suffix);
    elseif i < 100
        filename_inst = strcat(prefix,'000',Nstring,suffix);
    elseif i < 1000
        filename_inst = strcat(prefix,'00',Nstring,suffix);
    elseif i < 10000
        filename_inst = strcat(prefix,'0',Nstring,suffix);
    else
        filename_inst = strcat(prefix,Nstring,suffix);
    end

with

    Nstring = sprintf('%s%05d%s', prefix, i, suffix);
    

[Monique Embury]

Thank you for that tip! I have attached a link for a sample set of files I use. It will not let me upload them here due to their format.

https://drive.google.com/drive/folders/1tGTft5WxcCLie2_clGM16Psw2VTsRkpZ?usp=sharing