MATLAB: How to interpolate to the nearest value

integrationinterpolation

I have vector, v=(x,Y) and I want to find the nearest value of 'x' for C=(1,yi) rather than the interpolated values of xi's .I can find the interpolated value but taking the nearest values of x is difficult for me. Can you help me with this?

Best Answer

If you look at the documentation of interp1, you'll see that nearest neighbor interpolation is an option:

interp1(x,y,xi, 'nearest')

Related Solutions

MATLAB: How to use inerpolation option with end values? If I use interp1 command it’s giving NaN as the output if input is out of the range. I want to use end values if input is out of the range

>> X = [1,2,3];
>> Y = [12,5000,12000];
>> interp1(X,Y,4,'nearest','extrap')
ans =  12000
>> interp1(X,Y,4,'linear','extrap')
ans = 19000

But note that you cannot pick a method like linear, spline, etc, and also limit the extrapolation to the end values:

>> interp1(X,Y,[0,1.5,4],'linear','extrap')  % linear -> not end values
ans =
   -4976    2506   19000
>> interp1(X,Y,[0,1.5,4],'nearest','extrap') % nearest -> not linear interpolated
ans =
      12    5000   12000

But you can easily select the interpolation method and limit to the end values, by simply using max and min:

>> max(Y(1),min(Y(end),interp1(X,Y,[0,1.5,4],'linear','extrap')))
ans =
      12    2506   12000

If you only need to extrapolate in one direction then you could set the extrapolation value:

>> interp1(X,Y,[1.5,4],'linear',Y(end))
ans =
    2506   12000

MATLAB: Create an interpolated grid

% new interpolated grid 

lonx=min_x:20:max_x;
laty=min_y:20:max_y;
[Xi,Yi]=meshgrid(lonx,laty);
bathymetry=interp2(XX,YY,ZZ,Xi,Yi);
%surf(XX,YY,ZZ);

%ZZ(ZZ>0)=nan; 

figure(1)
%pcolor(XX,YY,ZZ),shading interp ,colorbar;

pcolor(Xi,Yi,bathymetry),shading flat ,colorbar;  % if error transpose bathymetry and see
saveas(gcf,'bat_fine','eps');

Also you can striaght away try this:

clear;
format long e
%open file  xyz 
T=readtable('points.txt');
A=T{:,:};
X=A(:,1);
Y=A(:,2);
Z=A(:,3);
min_x=min(X);
max_x=max(X);
min_y=min(Y);
max_y=max(Y);
n=length(X);
% new interpolated grid 
lonx=min_x:20:max_x;
laty=min_y:20:max_y;
[Xi,Yi]=meshgrid(lonx,laty);
bathymetry=interp2(X,Y,Z,Xi,Yi);
ZZ = griddata(X,Y,Z,Xi,Yi);
%surf(XX,YY,ZZ);
%ZZ(ZZ>0)=nan; 
figure(1)
%pcolor(XX,YY,ZZ),shading interp ,colorbar;
pcolor(lonx,laty,bathymetry),shading flat ,colorbar;  % if error transpose the bathymetry 
saveas(gcf,'bat_fine','eps');

Best Answer

Related Solutions

MATLAB: How to use inerpolation option with end values? If I use interp1 command it’s giving NaN as the output if input is out of the range. I want to use end values if input is out of the range

MATLAB: Create an interpolated grid

Related Question