How do I get directional profile of 2D functions ?

Hi all,

I have a simple question : Let us define the function z = sqrt(x^2 + y^2) if r < 0.9 and r=0 else. I would like to plot the profile along a line defined by a polar angle A, see the figure within the code or enclosed :

[x,y] = meshgrid(-1:0.1:1);
z = sqrt(x.^2 + y.^2); % or it can be z = x+y or any f(x,y)...
z(sqrt(x.^2 + y.^2) > 0.9)=0; % set the area where z is defined
ax = axes;
h = imagesc(ax,-1:0.1:1,-1:0.1:1,z);
set(ax,'YDir','normal');
% The function is plotted
% Now we plot the line where I want to get the z-profile
A = 30; % in deg
x0 = cos(deg2rad(A));
y0 = sin(deg2rad(A));
hold on
plot(ax,[-x0 0 x0],[-y0 0 y0],'k-');

%end of code

I would like to get the profile along the black line direction. I have played with mesh, surf, etc.. but it does not give the result I want. But I am quite new at MATLAB...

Any help is appreciated :) B

Answer 1

[Star Strider]

One approach:

v = -1:0.1:1;
xline = x0*v;
yline = y0*v;
zline = sqrt(xline.^2 + yline.^2);
zline(zline > 0.9)=0;

figure(2)
plot3(xline, yline, zline)
grid on

[Bastien Rouzé]

Yeah I agree. But in the example, I created z. Let us imagine that we have imported the z-values matrix without any knowledge on the function z = f(x,y).

[Star Strider]

Then let us use the interp2 (link) function to get the values of the plotted surface corresponding to ‘xline’ and ‘yline’:

v = -1:0.1:1;
xline = x0*v;
yline = y0*v;
zline = interp2(x,y,z, xline, yline, 'linear');

figure(3)
plot3(xline, yline, zline)
grid on

This is actually easier. Note that the interpolation vectors (or matrices) must be the same size. It might also be necessary to provide an extrapolation value.