Finding X,Y coordinates after image rotation

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Anisha Jamil
Anisha Jamil 2021-7-22
评论： Simon Chan 2021-7-22
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

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回答（1 个）

Simon Chan
Simon Chan 2021-7-22
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
  2 个评论
Anisha Jamil
Anisha Jamil 2021-7-22
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
Simon Chan 2021-7-22
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

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