How to find data displayed in pcolor using coordinates?

Hi all,

I am trying to find the value displayed by pcolor in a specific coordinate.

rng(1)
z = randn(11);
x = -5:5;
y = -5:5;

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

xq = 1.25;
yq = 2.34;

pcolor(x,y,z);
hold on
scatter(xq,yq, 'k', 'filled');

How can I find the z-value at the point xq, yq?

I have been banging my head against the wall and can't figure it out.

Answer 1

[Benoit Espinola]

rng(1 ) 
z = randn(11 ); 
x = -5:5 ; 
y = -5:5 ; 
[X, Y] = meshgrid(x,y ); 
xq = [1.25, -4.5 -4.5 -4.5 -4.5 -4.5 -4.1 -4.9, 4.5 -6]; 
yq = [2.34, -4.5 -3.5 -3.1 -3.9 -4.5 -4.5 -4.5, 4.5 -6]; 
hP = pcolor(x,y,z ); 
hold on 
scatter(xq,yq, 'k', 'filled');
xlim([-6 6])
ylim([-6 6])

[~,Id_x] = min(abs(x'-xq));
flag = xq < x(Id_x);
Id_x(flag) = Id_x(flag)-1; % put it back in the "right square"
Id_x(Id_x<1) = []; %outside range

[~,Id_y] = min(abs(y'-yq));
flag = yq < y(Id_y);
Id_y(flag) = Id_y(flag)-1; % put it back in the "right square"
Id_y(Id_y<1) = []; %outside range

zq = z(Id_y', Id_x'); % note the coordinates here are inverted
zq = zq(:,1)'; % got lazy to find something more elegant

Paras Patel has shown me the right path to the solution. However, Matlab returns the nearest neighbour, which in some situations yields to the wrong "pixel".

Answer 2

[Paras Patel]

rng(1)
z = randn(11);
x = -5:5;
y = -5:5;
[X, Y] = meshgrid(x,y);
xq = 1.25;
yq = 2.34;
hP = pcolor(x,y,z);
hold on
scatter(xq,yq, 'k', 'filled');

dt = datatip(hP,0,0);
hP.DataTipTemplate.DataTipRows(3).Value   = hP.CData; 

One way to do this would be to insert a datatip on the image. See the code above - it's crude but simple.

[Benoit Espinola]

Thanks, this has lead me to the right direction... I don't know why Mathworks doesn't offer somethig ready to query datapoints in a pcolor... go figure...

PS:, I know I should NOT use pcolor, but it's easy-ish

[Benoit Espinola]

With the datatip, Matlab returns the nearest neighbour, which in some situations yields to the wrong "pixel".