How to Interpolate 3 variables?

I have a series of data sets engine rpm, bmep and the corresponding fuel flow.

I need to calculate fuel flow depending on engine rpm and bmep across a range of values.

I'm unsure of how to implement the appropriate interpolation.

Any help would be great..

Thanks

Answer 1

[Star Strider]

The interp2 function would likely be my first choice, although without seeing your data, it’s impossible for me to say for certain.

[Star Strider]

El Gordo’s Answer moved here...

Hi Star Strider

I've attached my data

Al

[Star Strider]

Your data can’t be use with gridded interpolation, but scattered interpolation works:

[D,T,R] = xlsread('fuel flow data.xlsx');

xd = D(:,1);
yd = D(:,2);
zd = D(:,3);
x = linspace(min(xd),max(xd));
y = linspace(min(yd),max(yd));
z = linspace(min(zd),max(zd));
[X,Y] = meshgrid(x, y);

F = scatteredInterpolant(xd,yd,zd);

xq = 3500;              % Sample Interpolation Points
yq = 10;                % Sample Interpolation Points
zq = F(xq,yq);          % Sample Interpolation Points

figure(1)
scatter3(xd, yd, zd, '.g')
hold on
plot3(xq, yq, zq, 'pb', 'MarkerSize',10)
hold off
grid on
xlabel('Speed')
ylabel('BMEP')
zlabel('Fuel Flow')

producing this plot:

The blue star is a sample interpolation point.

[El Gordo]

Thanks, Star that's great. Why would the data not work with gridded interpolation?

[Star Strider]

I’m not sure why I couldn’t get it to work with gridded interpolation, but since scattered interpolation works, I went with that and didn’t explore further. (I found your data interesting. That higher pressure results in higher fuel flow must have something to do with the stoichiometry of your engine.)

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