how plot a correct interpolation with surf plot?

Question

Philippe Corner 2020-3-31

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https://ww2.mathworks.cn/matlabcentral/answers/514368-how-plot-a-correct-interpolation-with-surf-plot

评论： Philippe Corner 2020-3-31

Im using the code:

load A_PRE.mat; %find it attached
load Aelec.mat; %find it attached
figure(1)
X=A_PRE(:,1);  Y=A_PRE(:,4); Z=A_PRE(:,5);
[xq,yq]=meshgrid(linspace(min(X),max(X),100),linspace(min(Y),max(Y),100));
zq=griddata(X,Y,Z,xq(:),yq(:),'linear');
[c,h]=contourf(xq,yq,reshape(zq,100,100),'LineStyle','none','LevelStep',100); 
hold on
plot(cotas(:,1),cotas(:,2),'k','linewidth',4) %elevation data
hold on
scatter(X,Y,'filled','k')
figure(2)
plot3(Aelec(:,2),Aelec(:,3),Aelec(:,4),'k','linewidth',2);
hold on
scatter3(A_PRE(:,2),A_PRE(:,3),A_PRE(:,4),'filled','k')
hold on
level=A_PRE;
x = level(:,2);  y = level(:,3); z = level(:,4); c = level(:,5);
yv = linspace(min(level(:,3)), max(level(:,3)), 100); 
zv = linspace(min(level(:,4)), max(level(:,4)), 100);
[Y,Z] = meshgrid(yv, zv);
X = griddata(y,z,x,Y,Z,'cubic'); 
C = griddata(y,z,c,Y,Z,'cubic');
yA = Aelec(:,3); zA = Aelec(:,4);
in = inpolygon(Y,Z,yA(1:end-1),zA(1:end-1));
Z(in) = nan;
surf(X, Y, Z, 'cdata',C);
shading interp

for plotting the contour:

using surf function and using X and Y coordinates for its location, but when a use the same view of the 2D contour it seems to be interpolated wrong, any ideas about what could be my mistake? how could a I get a contour plot for figure 2 as similar than figure 1.

As you see, the yellow values seems to be affected with the other data using surf plot, any idea about how to obtain the interpolation plot as similar as fig 1? Thanks in advance

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Answer 1

darova 2020-3-31

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编辑：darova 2020-3-31

在 MATLAB Online 中打开

It happens because of different scales of data. Don't know why MATLAB get confused about it (even linear interpolation)

scale and center your data before interpolation

sc = (max(z)-min(z))/(max(y)-min(y));
y = y - mean(y);
x = x - mean(x);
y = y*sc;
x = x*sc;
yv = linspace(min(y), max(y), 50); 
zv = linspace(min(z), max(z), 50);
[Y,Z] = meshgrid(yv, zv);
X = griddata(y,z,x,Y,Z,'cubic'); 
C = griddata(y,z,c,Y,Z,'cubic');

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darova 2020-3-31

在 MATLAB Online 中打开

You can scale them back

sc = (max(z)-min(z))/(max(y)-min(y));
y0 = mean(y);
x0 = mean(x);
y = (y-y0)*sc;
x = (x-x0)*sc;
yv = linspace(min(y), max(y), 50); 
zv = linspace(min(z), max(z), 50);
[Y,Z] = meshgrid(yv, zv);
X = griddata(y,z,x,Y,Z,'cubic');            % made a mistake before
C = griddata(y,z,c,Y,Z,'cubic');            % made a mistkae before
Y = Y/sc + y0;                              % scale back
X = X/sc + x0;
surf(X,Y,Z,'cdata',C)                       % plot original