Superimpose a quiver plot on top of a picture

Hi,

I want to superimpose vector field on top of a TIFF figure!! my vector fields are in '.struct' format, but apparently the vectors are always appear below the figure!! Does anyone know why this happen? & how to superimpose a quiver plot onto a figure?! Here is my code: close all clear all

U=load('VelU - 5m1p2s1.mat');
W=load('VelW - 5m1p2s1.mat')
img = imread('fc2_save_2014-11-17-213936-0000.tif');
 imagesc(img);

     hold on;

    X = U(1,1).x(20:1:64,20:1:64);
    Y = U(1,1).y(20:1:64,20:1:64);
    Velu = U(1,1).u(20:1:64,20:1:64);
    Velw = W(1,1).w(20:1:64,20:1:64);

     quiver(X,Y,Velu,Velw, 'y','linewidth',2);

Answer 1

[Chad Greene]

Your image is plotted with x and y in units of pixels (from 1 to 1024), but your quiver plot spans the range 0.15 to 0.45. Replace your imagesc line with

imagesc(unique(X),unique(Y),img);

[soroush]

Yes, changing the image range make it works finally! Thank you Chad!

[Chad Greene]

You should verify that those pixels are properly registered. That is, make sure that each pixel in img is assigned to the proper x and y coordinates.

Answer 2

[Chad Greene]

Sometimes stacking gets a little confused, especially depending on the renderer and Matlab distribution. You can try

h = quiver(X,Y,Velu,Velw, 'y','linewidth',2);
uistack(h,'top')

or place the arrows at a higher z value with quiver3 like this:

quiver3(X,Y,ones(Velu),Velu,Velw,zeros(Velu) 'y','linewidth',2);

[Chad Greene]

Oops, that should be

quiver3(X,Y,ones(size(Velu)),Velu,Velw,zeros(size(Velu)) 'y','linewidth',2);