Why is my griddedInterpolant not working properly?

Hi, I am kind of new to matlab, for the purpose of interpolating 3D tables I use the function griddedInterpolant. If I plot the original table using surf, it looks totally wrong if I compare it with the griddedInterpolant plot, can someone explain what I did wrong?

I have a 10x10 matrix of sample points: DUR5 =

Columns 1 through 8

    2.1300    6.0900    7.0100    7.5200    8.0600    8.8100    9.7300   10.4300
    1.9200    5.8600    6.7700    7.3100    7.9500    8.6000    9.5200   10.2000
    1.5000    5.7400    6.4000    7.0300    7.7800    8.4100    9.3500    9.9800
    0.1400    5.0900    6.0000    6.4700    7.1000    8.0400    9.1400    9.8400
   -0.1900    5.0400    6.0500    6.4700    7.0800    8.0400    9.0200    9.8900
   -0.3700    5.0400    5.9500    6.5200    6.9800    7.6600    9.0200   10.2900
   -0.8000    4.4300    5.7000    6.3000    6.6800    7.3400    8.8100   10.2200
   -1.2900    3.8900    5.3000    5.9800    6.6300    7.3400    8.6500   10.3600
   -2.0200    3.6600    4.7600    5.3900    6.4200    7.3600    8.9800   10.5000
   -2.2300    1.6200    3.3300    4.7800    5.2300    6.1200    8.4800   10.6200

Columns 9 through 10

   11.3200   12.3000
   11.0400   11.9100
   10.7300   11.6000
   11.1300   12.2800
   11.1100   12.0900
   11.3700   12.6100
   11.7200   12.6300
   11.9800   13.5900
   12.3700   13.3800
   12.3700   14.3700

X-axis: MGSTR =

     0     2     4     5     7    10    15    20    25    30

Y-axis: RPM =

Columns 1 through 7

           0         150         550         900        1000        1250        1500

Columns 8 through 10

        1750        2000        2500

F=griddedInterpolant({MGSTR,RPM},DUR5)

F =

griddedInterpolant with properties:

            GridVectors: {[0 2 4 5 7 10 15 20 25 30]  [1x10 double]}
                 Values: [10x10 double]
                 Method: 'linear'
    ExtrapolationMethod: 'linear'

The normal plot is given by the folling command: surf(MGSTR, RPM, DUR5) For the gridded plot I make a mesh: Xi=0:1:30 Yi=0:50:2500 [X,Y]=ndgrid(Xi,Yi) and then plot the gridded version: surf(X,Y,F(X,Y))

It look like it is some sort of mirrored image. Can anybody please help?

Answer 1

[Adam]

You need to transpose your DUR5 matrix when you use griddedInterpolant because you are giving it X and Y vectors, but your matrix is actually Y,X because it is rows first then columns as 2nd dimension. This is something that always catches me out and confuses me when going between an X, Y space and a rows, columns space of matrix data.

i.e.

F=griddedInterpolant({MGSTR,RPM},DUR5')

[Hylke Tijsma]

Thank you very much, it worked.