matlab smoothing data problem

Question

peter huang 2023-11-6

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2043577-matlab-smoothing-data-problem

评论： Mathieu NOE 2023-11-8

Hello matlab users

I have a 2-dimensional water depth data. When the value is negative, it is land (make_bathy)

I need to linearly smooth the relationship between land and water to prevent the difference in water depth from being too large.

As shown in plot_bathy.m (read the file in QA.zip)

Thanks in advance

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Answer 1

Mathieu NOE 2023-11-6

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hello

I am not sure to understand your plot and where the transition land / water can be seen

nevertheless , if you need to smooth a 2D surface , I like the two following Fex submissions

smoothn - File Exchange - MATLAB Central (mathworks.com)

smooth2a - File Exchange - MATLAB Central (mathworks.com)

code

clear all
dep=load('dep_shoal_inlet.txt');
[n,m]=size(dep);
dx=2.0;
dy=2.0;
x=[0:m-1]*dx;
y=[0:n-1]*dy;
x_sponge=[0 180 180 0 0];
y_sponge=[0 0 y(end) y(end) 0];
x_wavemaker=[240 260 260 240 240];
y_wavemaker=[0 0 y(end) y(end) 0];
wid=5;
len=6;
set(gcf,'units','inches','paperunits','inches','papersize', [wid len],'position',[1 1 wid len],'paperposition',[0 0 wid len]);
clf
figure(1),
pcolor(x,y,-dep),shading flat
cbar=colorbar;
    set(get(cbar,'ylabel'),'String',' -dep (m) ')
hold on
plot(x_sponge,y_sponge,'g--','LineWidth',2)
text(10,1000,'Sponge','Color','g')
plot(x_wavemaker,y_wavemaker,'w-','LineWidth',2)
text(270,1200,'Wavemaker','Color','w')
    
caxis([-10 3])
xlabel('x (m)')
ylabel('y (m)')
% print -djpeg inlet_shoal.jpg
%  smoothn  : Fex : https://fr.mathworks.com/matlabcentral/fileexchange/25634-smoothn?s_tid=ta_fx_results
deps = smoothn(dep,1e5);
figure(2),
pcolor(x,y,-deps),shading flat
%  smooth2a  : Fex : https://fr.mathworks.com/matlabcentral/fileexchange/23287-smooth2a?s_tid=srchtitle
deps2 = smooth2a(dep,25,25);
figure(3),
pcolor(x,y,-deps2),shading flat

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Mathieu NOE 2023-11-7

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no problem

the code below is quite the same as above , adapted to plot_bathy.m

this is the result obtained with smoothn

smoothn - File Exchange - MATLAB Central (mathworks.com)

and with smooth2a

smooth2a - File Exchange - MATLAB Central (mathworks.com)

 clear all;clc;clf
 set(gcf,'color','w')
 %%
 m = 1024;
 n =  512;
 %---------------------grid size----------------------
 dx = 2.0;
 dy = 2.0;
 lx      = (n-1)*dx;
 ly      = (m-1)*dy;
 xx      = [0:dx:lx]';
 yy      = [0:dy:ly]';
 
 [x,y] = meshgrid(xx,yy);
  nx      = length(xx); % Mglob 
 ny      = length(yy); % Nglob
 %% initial water depth
 h0 = 10.0;
 
 %% iobs - index  ; water = 1
 for j = 1 : n
   for i = 1 : m     
      if ( x(i,j) >= 500 && x(i,j)<= 1024 && y(i,j)>= 1200 && y(i,j)<= 2048  )
       dep(i,j) = -2;
      elseif  ( x(i,j) >= 500 && x(i,j)<= 1024 && y(i,j)>= 0 && y(i,j)<= 1000  )
        dep(i,j) = -2;
      else
        dep(i,j) = h0; 
      end
   end
 end
 %%  check results
 figure(1),
  pcolor(x,y,-dep);shading interp ;colorbar  
 xlabel('x (m)')
 ylabel('y (m)')
 axis equal
 
 %  smoothn  : Fex : https://fr.mathworks.com/matlabcentral/fileexchange/25634-smoothn?s_tid=ta_fx_results
deps = smoothn(dep,1e5);
figure(2),
pcolor(x,y,-deps),shading interp ;colorbar 
 xlabel('x (m)')
 ylabel('y (m)')
 axis equal
 
%  smooth2a  : Fex : https://fr.mathworks.com/matlabcentral/fileexchange/23287-smooth2a?s_tid=srchtitle
deps2 = smooth2a(dep,20,30);
figure(3),
pcolor(x,y,-deps2),shading interp ;colorbar 
 xlabel('x (m)')
 ylabel('y (m)')
 axis equal
  