contour plotting in matlab

Hi

I have plotted a scattered plot and a contour plot (figure attached below). However, the contour plot has unusual curvy edges as marked in the figure. How to avoid these curvy edges and make a smooth color variation.

[Walter Roberson]

After you interpolate, use a low-pass filter?

[Bjorn Gustavsson]

What did you see when you looked at the triangulation around one of the intersections between the circle-sections and the horizontal lines?

[mukesh bisht]

Hi @Walter Roberson & @Bjorn Gustavsson.

I have attached my data and code. Please suggest how to use a low-pass filter. When I look at the intersection it shows dark coloured patches (figgure attached).

Note: In actual figure i have rotated my axes to plot data, but i have not included the roated data in file attached (which doesnt matter here).

Code:

x = D(:,1);y = D(:,2);z = D(:,3);
xv = linspace(min(x), max(x),1000); yv = linspace(min(y), max(y),1000);
[Xm,Ym] = ndgrid(xv, yv);
Zm = griddata(x, y, z, Xm, Ym,'natural');
hold on
figure(15)
contourf(Xm, Ym, Zm, 200, 'LineStyle','none'); colormap jet; colorbar

[Bjorn Gustavsson]

You should first figure out why you get these "pricks" in the first place. Then figure out a way to handle that cause. Here's what you should do, explicitly.

On top of your scatterplot plot the edges of all the triangles created by the triangulation used by delaunay, which is used inside the griddata/scatteredinterpolant/triscatteredinterpolant functions, like this:

tri = delaunay(x,y);
clf
% Your call to scatter goes here
hold on
edges = [1 2;2 3;3 1];
for i1 = 1:size(tri,1)
  for i2 = 1:3
    h = plot(x(tri(i1,edges(i2,:))),y(tri(i1,edges(i2,:))),'b','linewidth',2);
    drawnow
    set(h,'linewidth',1)
  end
end

Then you zoom in onto the edge between the "all-blue" circle-sectors and the lines - there you will see the cause of your problem.

[Bjorn Gustavsson]

Well I guess you could also go for a non-linear diffusion-filter but that will be for later when other means to handle your problem is exhausted.