## Hi all, i have a two circles in an image which are concentric, i used a command [x,y]=ginput(1). Using the mouse pointer i click on the one of the concentric circles,with reference to the [x,y] point how to find out the inner dia,outer dia,center

on 24 Dec 2012

on 30 Jun 2014

### Image Analyst (view profile)

Is it possible to draw a circle with reference to the {[x,y]=ginput(1)} single point.

Matt J

### Matt J (view profile)

on 24 Dec 2012

Explain what that means.

Walter Roberson

### Walter Roberson (view profile)

on 24 Dec 2012

Should the largest circle be drawn from the starting point, that just touches one (or both) of the two concentric circles ?

Walter Roberson

on 26 Dec 2012

## Products

### Image Analyst (view profile)

on 28 Dec 2012

Here's how to do it with ginput(1), rather than automatically, just like you asked for:

```clc;    % Clear the command window.
close all;  % Close all figures (except those of imtool.)
imtool close all;  % Close all imtool figures if you have the Image Processing Toolbox.
clear;  % Erase all existing variables. Or clearvars if you want.
workspace;  % Make sure the workspace panel is showing.
format long g;
format compact;
fontSize = 20;
```
```imshow('C:\Users\Naresh\Documents\Temporary\intq.png');
```
```% Ask for center using ginput(1)
message = sprintf('Please click at the center of the circles');
button = questdlg(message, 'Continue?', 'OK', 'Quit', 'OK');
drawnow;	% Refresh screen to get rid of dialog box remnants.
if strcmpi(button, 'Quit')
return;
end
[xCenter, yCenter] = ginput(1)
hold on;
markerSize = 30; % Size of the cross.
lineWidth = 2; % Thickness of the cross.
plot(xCenter, yCenter, 'r+', 'MarkerSIze', markerSize, 'LineWidth', lineWidth);
```
```% Ask for inner edge using ginput(1)
message = sprintf('Please click at the inner edge of the circles');
button = questdlg(message, 'Continue?', 'OK', 'Quit', 'OK');
drawnow;	% Refresh screen to get rid of dialog box remnants.
if strcmpi(button, 'Quit')
return;
end
[xInner, yInner] = ginput(1)
% Draw a cross at the point where they clicked.
plot(xInner, yInner, 'r+', 'MarkerSIze', markerSize, 'LineWidth', lineWidth);
% Draw a line to it.
line([xCenter, xInner], [yCenter, yInner], 'Color', 'b', 'LineWidth', lineWidth);
```
```% Calculate diameter:
innerDiameter = sqrt((xInner-xCenter)^2+(yInner-yCenter)^2)
```
```% Ask for outer edge using ginput(1)
message = sprintf('The inner diameter = %.2f\n\nPlease click at the outer edge of the outer circles', innerDiameter);
button = questdlg(message, 'Continue?', 'OK', 'Quit', 'OK');
drawnow;	% Refresh screen to get rid of dialog box remnants.
if strcmpi(button, 'Quit')
return;
end
[xOuter, yOuter] = ginput(1)
plot(xOuter, yOuter, 'r+', 'MarkerSIze', markerSize, 'LineWidth', lineWidth);
% Draw a line to it.
line([xCenter, xOuter], [yCenter, yOuter], 'Color', 'b', 'LineWidth', lineWidth);
```
```% Calculate diameters:
outerDiameter = sqrt((xOuter-xCenter)^2+(yOuter-yCenter)^2)
innerDiameter = sqrt((xInner-xCenter)^2+(yInner-yCenter)^2)
```
```message = sprintf('The outer diameter = %.2f\nThe inner diameter = %.2f',...
outerDiameter, innerDiameter);
uiwait(helpdlg(message));
```

### Image Analyst (view profile)

on 25 Dec 2012

See the FAQ: http://matlab.wikia.com/wiki/FAQ#How_do_I_create_a_circle.3F for code on how to draw circles and ellipses.

Image Analyst

### Image Analyst (view profile)

on 28 Dec 2012

I do it that way in my answer elsewhere in this post. I give you full turnkey code for doing it.

Naresh Naik

### Naresh Naik (view profile)

on 31 Dec 2012

Good Morning Sir, The above matlab code giving the output by manually we are selecting center ,inner and outer diameter from these information we are finding the ID,OD and it's Center.

But without selecting center ,ID and it's OD can we do the same job?

i mean you can select any one of the circle from that we can get (x,y) co-ordinate and intensity value of that image can we find out the center ,ID and OD. Note: Do not use [x,y]=ginput(1) more than once in a programme. Is this possible to solve through matlab code?

Image Analyst

### Image Analyst (view profile)

on 31 Dec 2012

We've talked about that already. If you don't want to do it manually with ginput, then there are ways with thresholding and regionprops to find things automatically. You could also combine them if you want to find, say, just one pair of diameters rather than the whole set.

### Walter Roberson (view profile)

on 25 Dec 2012

With regards to your current version of the question asking whether it is possible to draw a circle with reference to ginput(1) coordinates, the answer is YES, and the method is as linked to by Image Analyst in the FAQ.

### Walter Roberson (view profile)

on 25 Dec 2012

The question you emailed me involved finding the inner and outer diameter of circles within a "bulls-eye" type pattern, and wanting to know how to find a diameter of a circle pointed to using ginput()

I would suggest that you just find all of the inner and outer diameters and then worry about the output.

To find the diameters, start by thresholding the image using "<" so that you get "true" for the dark areas. Then bwlabel() the binary image that results. regionprops() that, and request the Area and the FilledArea and the EquivDiameter. The EquivDiameter will give you the outer diameter. sqrt((Area - FilledArea) / pi) is the inner diameter and will be 0 for the innermost circle. Sort by EquivDiameter to get the order of the circles.

If you still want the user to be able to click to choose a particular point, then after the click, extract that same point from the labeled image, and the label will tell you the array index of regionprops results.

Image Analyst

### Image Analyst (view profile)

on 28 Dec 2012

You saw his answer: above - you even responded to it so I'm not sure why you are asking again.

Image Analyst

### Image Analyst (view profile)

on 29 Dec 2012

Like I said in another comment, see my code below where I use the manual method of ginput(1) like you asked for.

Walter Roberson

### Walter Roberson (view profile)

on 29 Dec 2012

As I wrote above "The EquivDiameter will give you the outer diameter"

### Bikram (view profile)

on 30 Jun 2014

Hi All, I have a power spectrum of an image.I want to divide the spectrum into five concentric circles. Then I want to plot energy vs radius of those regions. Would you please help me. Thanks