Finding X,Y coordinates after image rotation

Hello, I am trying to find the values of some selected points with xy coordinates after rotating an image (90,180,270).

The following code lets me select an option for rotation. Therefore, I created a loop.

Could someone please tell me if my equations are correct?

x1,y1 is the coordinate of a point and x2,y2 is the coordinate of the same point after rotation.

[m,n]=size(image);
         % Need rotate?
        prompt = {'no rotation: 0; counter clockwise 90: 1, counter clockwise 180: 2,counter clockwise 270: 3'};
        dlgtitle = 'Need rotate?';
        definput = {'0'};
        answer2 = str2double(char(inputdlg(prompt,dlgtitle,[1,80],definput)));

        if answer2 == 0
            moving = moving;
            x2=x1;
            y2=y1;
        elseif answer2 == 1
            moving = rot90(moving,1);
            x2=y1;
            y2=n-x1;
        elseif answer2 == 2
            moving = rot90(moving,2);
            x2=m-x1;
            y2=n-y1;
        elseif answer2 == 3
            moving = rot90(moving,3);
            x2=n-y1;
            y2=x1;
        else
            msg = 'invalid input!';
            error(msg)
        end

Answer 1

[Simon Chan]

The following code is going to check the coordinates and not replacing your code, so you may need to verify you code based on the result:

clear; clc;
m = 25; n = 20;
BW = zeros(m,n);
x1=9; y1=7;
BW(y1,x1)=1;                                            % Put one white dot in the image
Result{1} = BW;                                         
Result{2} = rot90(BW,1);
Result{3} = rot90(BW,2);
Result{4} = rot90(BW,3);
[y2, x2] = cellfun(@(x) ind2sub(size(x),find(x)),Result);

And the result shown as follows:

x2 =
     9     7    12    19 
  % x1    y1    n-x1+1    m-y1+1
y2 =
     7    12    19     9 
  % y1    n-x1+1    m-y1+1    x1

[Anisha Jamil]

Thank you so much! I'm also trying to find the coordinates after flipping the same image. Could you please help me cross check this too?

% Need flip?

prompt = {'no flip: 0; leftside right: 1, upside down:2, both: 3'};

dlgtitle = 'Need flip?';

definput = {'0'};

answer1 = str2double(char(inputdlg(prompt,dlgtitle,[1,60],definput)));

if answer1 == 0

moving = moving;

x1=x;

y1=y;

elseif answer1 == 1

moving = fliplr(moving);

x1= m-x+1;

y1=y;

elseif answer1 == 2

moving = flipud(moving);

x1=x;

y1=n-y;

elseif answer1 == 3

moving = fliplr(flipud(moving));

x1=m-x+1;

x1=n-y;

else

msg = 'invalid input!';

error(msg)

end

[Simon Chan]

I think you are able to verify easily by slightly modifying my previous code:

m = 25; n = 20;
BW = zeros(m,n);
x1=9; y1=7;
BW(y1,x1)=1;
Result{1} = BW;
Result{2} = fliplr(BW);
Result{3} = flipud(BW);
Result{4} = fliplr(flipud(BW));
[y2, x2] = cellfun(@(x) ind2sub(size(x),find(x)),Result)

Result:

y2 =
     7     7    19    19
 %%  y1    y1    m-y1+1    m-y1+1
 
x2 =
     9    12     9    12 
 %% x1    n-x1+1    x1    n-x1+1