ImagePosition, FigPosition, and AxisPosition perplexity

Hello,

How to get the coordinates of the 4 corners of an image within a figure,

and how it relates to the figure position, the axis position, the xlimits, the ylimits, and possibly the PlotBoxAspectRatio.

also:

imshow('saturn.png');

% then eventually manipulate the figure position, the axis position, the xlim, the ylim.

%

% Why the following code below fails to get the proper image corners (lower left x-y point, width, height),

% in pixel units ?

axlim = get(gca,'Position')

fglim = get(gcf,'Position')

x1 = axlim(1)*fglim(3) + fglim(1);

x2 = (axlim(1)+axlim(3))*fglim(3) + fglim(1);

y1 = axlim(2)*fglim(4) + fglim(2);

y2 = (axlim(2)+axlim(4))*fglim(4) + fglim(2);

Thanks,

[Rik]

I'm not entirely certain the size of the axes object will change if the image requires a smaller window. You might need to get the position of the image object (perhaps by querying the XData and YData properties).

Answer 1

[Sandeep Mishra]

Hi francois,

I understand that you want to find the four corners of an image within a figure.

To implement this, you can fetch the X and Y axis limits of the current axis using ‘XLim’ and ‘YLim’ property and based on that you can calculate the width and height of the image.

Refer to the following example code snippet to find the image corners:

% Load and display the image 
img = imread('saturn.jpg'); 
imshow(img); 

% Fetch axes limits 
x_limits = get(gca, 'XLim');  
y_limits = get(gca, 'YLim');  

% Finding image staring points 
x_start = x_limits(1);  
y_start = y_limits(1);  

% Calculating width and height of the image 
width = x_limits(2) - x_limits(1);  
height = y_limits(2) - y_limits(1); 

% Image coordinates 
image_coordinates = [ 
    x_start, y_start; 
    x_start + width, y_start; 
    x_start + width, y_start + height; 
    x_start, y_start + height 
    ]; 

For more information, refer to the following MathWorks Documentation:

1. ‘XLim' property: /https://www.mathworks.com/help/releases/R2024b/matlab/ref/xlim.html
2. ‘YLim’ property: https://www.mathworks.com/help/releases/R2024b/matlab/ref/ylim.html

I hope this helps!