How to generate gifs using countourf and mutliply file inputs?

Hello everyone

I have multiple binary inputs files with which I would like to generate a gif using countourf. The mutiply binary files are representing a solution to each timestep where the number of the timestep can vary. Each binary files is saved as "0_100_S_timestep_1.bin" ,"0_100_S_timestep_2.bin" and so one where the integer number at the end indicates the time step. Right now I try to generate the gif using the following code:

clear; 
clc;
close('all')
x0=10;
y0=250;
width=1000;
height=200;

figure('Name', 'Temperature field')
fid = fopen('0_100_T_result.bin');
nx = fread(fid,1,'int32');
ny = fread(fid,1,'int32');
T = reshape(fread(fid,nx*ny,'double'),nx,ny);
fclose = (fid);
contourf(T')
colorbar;

set(gcf,'position',[x0,y0,width,height])
saveas(gcf,'T_10.png');

figure('Name', 'Streamfunction field')
fid = fopen('0_100_S_result.bin');
nx = fread(fid,1,'int32');
ny = fread(fid,1,'int32');
S = reshape(fread(fid,nx*ny,'double'),nx,ny);
fclose = (fid);
contourf(S')
colorbar;
set(gcf,'position',[x0,y0,width,height])
saveas(gcf,'Streamfunction_10.png');

figure('Name', 'Vorticity field')
fid = fopen('0_100_W_result.bin');
nx = fread(fid,1,'int32');
ny = fread(fid,1,'int32');
W = reshape(fread(fid,nx*ny,'double'),nx,ny);
fclose = (fid);
contourf(W')
colorbar;
set(gcf,'position',[x0,y0,width,height]);
saveas(gcf,'Vorticity_10.png');

load 0_100_uymax_vs_time.data;
load 0_100_uxmax_vs_time.data;
figure('Name', 'umax over time')
hold on
plot(X0_100_uxmax_vs_time,'DisplayName','ux_{max}');
plot(X0_100_uymax_vs_time,'DisplayName','uy_{max}');
ylabel('velocity')
xlabel('time')
legend
hold off

width=550;
height=400;
set(gcf,'position',[x0,y0,width,height])
saveas(gcf,'umax_vs_time_10.png');


h = figure;
filename = 'gif_10.gif';
for t=1:70  % t is the percent number in the file name
    subplot(311)
    fn = "0_100_T_timestep_"+t+".bin";
    fid = fopen(fn);       % file for t-th step
    nx = fread(fid,1,'int32');
    ny = fread(fid,1,'int32');
    T = reshape(fread(fid,nx*ny,'double'),nx,ny);
    fclose = (fid);
    contourf(T');
    colorbar;
    title('Temperature') ;
    
    subplot(312)
    fn = "0_100_S_timestep_"+t+".bin";
    fid = fopen(fn);       % file for t-th stepfid = fopen('S.bin');
    nx = fread(fid,1,'int32');
    ny = fread(fid,1,'int32');
    S = reshape(fread(fid,nx*ny,'double'),nx,ny);
    fclose = (fid);
    contourf(S');
    colorbar;
    title('Streamfunction') ;

    subplot(313)
    fn = "0_100_W_timestep_"+t+".bin";
    fid = fopen(fn);       % file for t-th stepfid = fopen('S.bin');
    nx = fread(fid,1,'int32');
    ny = fread(fid,1,'int32');
    W = reshape(fread(fid,nx*ny,'double'),nx,ny);
    fclose = (fid);
    contourf(W');
    colorbar;
    title('Vorticity') ;
    
    % Capture the plot as an image 
      frame = getframe(h); 
      im = frame2im(frame); 
      [imind,cm] = rgb2ind(im,256); 
      % Write to the GIF File 
      if t == 10 
          imwrite(imind,cm,filename,'gif', 'Loopcount',inf); 
      else 
          imwrite(imind,cm,filename,'gif','WriteMode','append'); 
      end 
    pause(0.2)
end

I however get now the following error message:

Warning: Contour not rendered for constant ZData 
> In contourf (line 60)
In matlab_0_1 (line 81) 
Error using wgifc
Can only append to GIF89a format GIFs.

Error in writegif (line 306)
wgifc(mat, map, filename,writemode,disposalmethod,delaytime,...

Error in imwrite (line 566)
        feval(fmt_s.write, data, map, filename, paramPairs{:});

Error in matlab_0_1 (line 104)
          imwrite(imind,cm,filename,'gif','WriteMode','append');
          

and now gif is created. How can I resolve this? And also how can I make the for loop such that it goes automatically over all time step until largest timestep in the files available?

All help is creatly appriaciated and many thanks already in advance.

Answer 1

[Samay Sagar]

Hi David,

The warning about constant “ZData” in the “contour” function suggests that at least one of your binary files may contain uniform data, which cannot produce a contour plot.

The error with “imwrite” indicates a problem with appending frames to the GIF file. The initial frame must be saved in the GIF89a format with the “Loopcount”, inf property to establish the animation. Subsequent frames should then be appended with “WriteMode”, “append”.

To automate the process of iterating over all available timesteps, you can utilize MATLAB's file listing functions to dynamically determine the number of timesteps.

Here’s how you can update your code:

clear; 
clc;
close('all');

x0 = 10;
y0 = 250;
width = 1000;
height = 200;

filename = 'gif_10.gif';
h = figure('position', [x0, y0, width, height * 3]);

% Get a list of all files that match the pattern
files = dir('0_100_T_timestep_*.bin');
numFiles = length(files);

for i = 1:numFiles
    % Extract the timestep number from the file name
    [~, name, ~] = fileparts(files(i).name);
    parts = strsplit(name, '_');
    timestep = str2double(parts{end});
    
    % Read and plot Temperature
    subplot(311);
    dataT = readBinaryData(['0_100_T_timestep_' num2str(timestep) '.bin']);
    contourf(dataT');
    colorbar;
    title('Temperature');
    
    % Read and plot Streamfunction
    subplot(312);
    dataS = readBinaryData(['0_100_S_timestep_' num2str(timestep) '.bin']);
    contourf(dataS');
    colorbar;
    title('Streamfunction');
    
    % Read and plot Vorticity
    subplot(313);
    dataW = readBinaryData(['0_100_W_timestep_' num2str(timestep) '.bin']);
    contourf(dataW');
    colorbar;
    title('Vorticity');
    
    % Capture the plot as an image 
    frame = getframe(h); 
    im = frame2im(frame); 
    [imind, cm] = rgb2ind(im, 256); 
    
    % Write to the GIF File 
    if i == 1
        imwrite(imind, cm, filename, 'gif', 'Loopcount', inf);
    else
        imwrite(imind, cm, filename, 'gif', 'WriteMode', 'append');
    end
    
    pause(0.2);  % Adjust this pause as needed
end

% Helper function to read binary data
function data = readBinaryData(filename)
    fid = fopen(filename, 'r');
    nx = fread(fid, 1, 'int32');
    ny = fread(fid, 1, 'int32');
    data = reshape(fread(fid, nx * ny, 'double'), nx, ny);
    fclose(fid);
end

The above script now includes a helper function “readBinaryData” that reads the binary data files for temperature, streamfunction, and vorticity. It also automatically loops over all files that match the pattern “0_100_T_timestep_*.bin”. Adjust the pattern as necessary for your specific filenames.

For additional information about “imwrite” and “contourf” please refer to the following documentation:

https://www.mathworks.com/help/releases/R2021b/matlab/ref/imwrite.html

https://www.mathworks.com/help/releases/R2021b/matlab/ref/contourf.html