Bilinear Interpolation in Matlab

Bilinear Interpolation in Matlab

(Applied Mathematics)

%3-D interpolation for the use of fuel maps in Engine Control Units (ECUs)

%Develped by Ransalu Senanayake (20-03-2011)

%HELP: fmap(desired_x_value, desired_y value)

function[]=fmap2(realx,realy)

help fmap2

nearx=realx-rem(realx,10);

neary=realy-rem(realy,10);

x=0:10:100;

y=0:10:100;

xval=find(x==nearx);

yval=find(y==neary);

%ploting the fuel map - Assuming desired map is given by z

x=0:10:100;

y=0:10:100;

[X,Y]=meshgrid(x,y);

z=X.*exp(-(X/60).^2-(Y/60).^2);

Z=(z)*100/max(max(z(:)));

surf(X,Y,Z)

view([0 0 180])

xlabel('x-axis')

ylabel('y-axis')

zlabel('z-axis')

title('Fuel Map')

%4 neighbours

x1y1=Z(yval,xval);

x2y1=Z(yval,xval+1);

x1y2=Z(yval+1,xval);

x2y2=Z(yval+1,xval+1);

appears_as=[x1y2 x2y2;x1y1 x2y1]

%finding zy

zy1=((nearx+10-realx)*x1y1+(realx-nearx)*x2y1)/10;

zy2=((nearx+10-realx)*x1y2+(realx-nearx)*x2y2)/10;

zy=((neary+10-realy)*zy1 + (realy-neary)*zy2)/10;

%matlab interpolation

m=0:1:100; n=0:1:100;

[M,N]=meshgrid(m,n);

P=interp2(X,Y,Z,M,N);

%figure, mesh(M,N,P)

Matlab_ans = P(realy+1,realx+1);

%calculating errors

answer_is=zy;

answer_shoud_be=realx*exp(-(realx/60)^2-(realy/60)^2)*100/max(max(z(:)));

my_percentage_error=100*(answer_shoud_be-answer_is)/(max(appears_as(:))-min(appears_as(:)));

Matlab_percentage_error=100*(answer_shoud_be-Matlab_ans)/(max(appears_as(:))-min(appears_as(:)));

%console display

disp(['Answer should be: ',num2str(answer_shoud_be)]);

disp(['My Answer is: ',num2str(zy), ' with error: ',num2str(my_percentage_error),'%'])

disp(['Matlab Answer is: ',num2str(Matlab_ans), ' with error: ',num2str(Matlab_percentage_error),'%'])