CODEWITHSUNDEEP
matlabinterpolation
HCAI
HCAI

Reputation: 2263

Interpolation of data to a staggered grid

I have data on 25 points like this:

Z=

0.6840    0.7208    1.0240    1.0293    0.7713
0.8602    0.9089    1.3414    0.8970    0.7107
0.8869    0.8282    1.7015    0.9967    0.9243
0.7469    0.9534    1.5206    1.2741    1.0281
0.8952    1.1554    0.8525    1.2993    0.9890

pcolor(Z)=

enter image description here

Pcolor interpolates the data to form the colours but doesn't give me the value of each new square. I'd like to do this manually via interpolation:

I'd like to average these pink points to make an interpolated value at the centre of each square ie the blue numbers.

enter image description here

This doesn't seem to do that.

x=1:5;
y=1:5;

xi=0.5:1:5;
yi=0.5:1:5;
ZI=interp2(x,y,Z,xi,yi);

gives: ZI =

0.8918    1.0778    0.8194       NaN       NaN
0.9084    1.3375    0.8967       NaN       NaN
1.0035    1.5858    0.8852       NaN       NaN
1.1633    1.4250    1.0040       NaN       NaN
   NaN       NaN       NaN       NaN       NaN

Any pointers would be appreciated, Regards,

Upvotes: 0

Views: 1119

Answers (1)

leonbloy
leonbloy

Reputation: 75896

It's not clear if you want an supersampled matrix or just the interpolated values. If the later, you could simply do:

 Z = [ 0.6840 ,   0.7208   , 1.0240   , 1.0293  ,  0.7713;
       0.8602  ,  0.9089  ,  1.3414  ,  0.8970  ,  0.7107;
       0.8869  ,  0.8282  ,  1.7015  ,  0.9967  ,  0.9243;
       0.7469  ,  0.9534  ,  1.5206  ,  1.2741  ,  1.0281;
       0.8952  ,  1.1554  ,  0.8525  ,  1.2993  ,  0.9890];

 Z1 = (Z(1:end-1,1:end-1)+Z(2:end,1:end-1)+Z(1:end-1,2:end)+Z(2:end,2:end))/4

ans =

   0.79348   0.99877   1.07293   0.85208
   0.87105   1.19500   1.23415   0.88218
   0.85385   1.25093   1.37322   1.05580
   0.93773   1.12047   1.23662   1.14762

Or if you really want to use the interp2 function: (I use a 5x4 matrix so that it's more instructive)

 Z = [ 0.6840 ,   0.7208   , 1.0240   , 1.0293  ,  0.7713;
       0.8602  ,  0.9089  ,  1.3414  ,  0.8970  ,  0.7107;
       0.8869  ,  0.8282  ,  1.7015  ,  0.9967  ,  0.9243;
       0.7469  ,  0.9534  ,  1.5206  ,  1.2741  ,  1.0281]

   interp2(Z,[1:4 ]+0.5,[1:3]'+0.5) 

   0.79348   0.99877   1.07293   0.85208
   0.87105   1.19500   1.23415   0.88217
   0.85385   1.25093   1.37322   1.05580

(tested in Octave)

Upvotes: 2

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