How to flip an axis on a plot without affecting the plot?

I am trying to rotate the y axis of this plot such that the origin is at the upper left coner of the plot. How would I do so?

This is the code I have to set up my plot.

% Plot averaged vector field
figure(3)
quiver(x(acceptIdx)/48.11,(y(acceptIdx)/48.11),u_avg(acceptIdx),v_avg(acceptIdx),4)
axis([0 42 0 42])
yticks([0 5 10 15 20 25 30 35 40])
set(gca,'XAxisLocation','top','YAxisLocation','left');
xlabel('z (mm)')
ylabel('x (mm)')
title('Dimensional velocity field')

I'd like the y axis to look identical to the x axis.

Thanks.

Answer 1

[meghannmarie]

Try:

axis(gca,'ij')

[Monique Embury]

That flips the whole image as well.

[meghannmarie]

Are you sure you want to move your data points to new locations? If so, I think you would have to transform your data.

[Monique Embury]

I just want to change the appearance of the axis. When the photos were taken, the origin of the shot was the bottom left corner, but for presenting the information, it should be at the top left corner.

[meghannmarie]

Would flipping the labels work for you? Try this:

gca.YtickLabel = flipud(gca.YTickLabel);

[Monique Embury]

I get this error:

Undefined function or variable 'gca'.

Error in piv_averages (line 120)
gca.YtickLabel = flipud(gca.YTickLabel);

[meghannmarie]

Im sorry, try this:

ax = gca;
ax.YTickLabel = flipud(ax.YTickLabel);

[Monique Embury]

Wonderful! It worked!

Answer 2

[Ni2]

Add this code

set(gca, 'YDir','reverse')

After the plot command

[Monique Embury]

The plot looks the same.

[Ni2]

Try this code

    k = (min(y) + max(y))/2;
    newy = 2*k - y;
    plot(x,newy);
    set(gca, 'YDir', 'reverse')

Here i have considered your x-axis variable is 'x' and initial y-axis variable is 'y'

Final y-axis variable is considered to be 'newy'

[Monique Embury]

This did not work.

[Ni2]

Can u send me your codes

[Monique Embury]

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=3.007; %speed of sound
x0=1024; %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);             % x-position (mm)
    y = A_inst(:,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

% 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 = 400; %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(4)
quiver(x(acceptIdx), y(acceptIdx), u_avg(acceptIdx), v_avg(acceptIdx), 5)
% add reference line at threshold if you'd like
line(x,yThreshold); 

% Plot nondimensional vector field
figure(2)
quiver(x_non(acceptIdx),y_non(acceptIdx),u_non(acceptIdx),v_non(acceptIdx),4)
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('x/D')
ylabel('y/d')
title('Nondimensional velocity field')

% Plot averaged vector field
figure(1)
quiver(x(acceptIdx),y(acceptIdx),u_avg(acceptIdx),v_avg(acceptIdx),4)
axis([0 2000 0 2000])
set(gca,'YtickLabel',2000:-200:0)
set(gca,'XAxisLocation','top','YAxisLocation','left');
xlabel('z (pixels)')
ylabel('x (pixels)')
title('Dimensional velocity field')

% Plot averaged vector field
figure(3)
quiver(x(acceptIdx)/48.11,(y(acceptIdx)/48.11),u_avg(acceptIdx),v_avg(acceptIdx),4)
axis([0 42 0 42])
yticks([0 5 10 15 20 25 30 35 40])
set(gca,'XAxisLocation','top','YAxisLocation','left');
% set(gca,'ydir','reverse')
xlabel('z (mm)')
ylabel('x (mm)')
title('Dimensional velocity field')

% Output averaged data
output_avg = [x y u_avg v_avg CHC_tot];
dlmwrite('average_vels.dat','xyUVC');
dlmwrite('average_vels.dat',output_avg,'-append');

[zhou weiyan]

Thank you so much!