How to smoothly interpolate between distant points in 2D matrix?

Hey guys,

I have a matrix such as A = [0 0 0 0 0 0;0 5 7 0 9 0;0 0 0 0 0 0;0 0 0 0 0 0;0 0 0 0 0 0;0 0 5 0 0 0;0 3 0 0 6 0;1 0 0 0 0 0]; as I only have some measurements in the area 8x6, points without measurements are zero.

Now I want to interpolate between the points where I have data (>0) using the following:

 %if true
[X,Y] = meshgrid(1:1:6,1:1:8);
[Xq,Yq] = meshgrid(1:0.1:6,1:0.1:8);
Vq = interp2(X,Y,A,Xq,Yq);
surf(Xq,Yq,Vq)
 %end

This is the product:

The question is, how can I only interpolate between the points with values >0 ("connect the peaks"? If I try to set all zeros as NaN the result is even worse...

Thanks a lot for your help!

Valle

Answer 1

[John D'Errico]

1. Replace the zeros with NaNs.

2. Use my inpaint_nans tool, found on the File Exchange.

A(A==0) = NaN
A =
   NaN   NaN   NaN   NaN   NaN   NaN
   NaN     5     7   NaN     9   NaN
   NaN   NaN   NaN   NaN   NaN   NaN
   NaN   NaN   NaN   NaN   NaN   NaN
   NaN   NaN   NaN   NaN   NaN   NaN
   NaN   NaN     5   NaN   NaN   NaN
   NaN     3   NaN   NaN     6   NaN
     1   NaN   NaN   NaN   NaN   NaN

B = inpaint_nans(A)
B =
       3.1888       5.5122       7.6469       9.0166       9.8404       10.513
       3.0913            5            7       8.1801            9       9.8074
       3.1825       4.7842       6.3775       7.5284       8.4156       9.2531
       3.2633        4.581        5.911       6.9897       7.8907       8.7576
       3.1307       4.2808       5.4915       6.4791       7.3464       8.2189
       2.6661       3.7807            5       5.8982        6.722       7.5883
       1.8903            3       4.1818       5.1491            6       6.8921
            1       2.2296       3.4176       4.4402       5.3339       6.2119

surf(B)

[Valentin]

Thanks a lot John, is working super-smoothly!