MATLAB Answers

Rotate the plot at 45 degree

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Sharah
Sharah on 29 Sep 2016
Answered: Jakub Rysanek on 4 Oct 2016
Can anyone tell me how to rotate the plot from the following image so that the now the linear reference line will be a straight vertical line, and the red and green line will fall on the left side of the plot?
for a reference the red and green line is just a data that I plot with different slope.

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Answers (2)

Jakub Rysanek
Jakub Rysanek on 4 Oct 2016
I would simply rotate all data using the planar (2D) transform with respect to the origin:
angle = pi/4;
reference_line = [0 1 2 3 4 5 6];
data_x = [0 1 2 3 4 5 6];
data_y = [0 1.1 2.2 3.3 4.4 5.5 6.6];
% 2D rotation
x2 = data_x*cos(angle)-data_y*sin(angle);
y2 = data_y*cos(angle)+data_x*sin(angle);
figure;
hold on;
p1=plot(reference_line,reference_line,'marker','none','linestyle','--');
p2=plot(data_x,data_y,'-r');
p3=plot(x2,y2,'-b');
p4=plot(zeros(1,7),reference_line,'-k');
set(gca,'ylim',[0 6],'xlim',[-6 6]);
axis square;
legend([p1,p2,p3,p4],{'Reference line','Original data','Rotated data','Vertical line'},'Location','southwest');

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Walter Roberson
Walter Roberson on 29 Sep 2016
Create an hgtransform, set the axes parent to be the transform, set the rotation matrix for the transform to have the appropriate rotation.
Note: this will transform the axes too, rotating the entire plot.
If you want just the data to be rotated then the easiest single way would probably:
[th, r] = cart2pol(x, y);
[nx, ny] = pol2cart(th+pi/4, r);
Your x and y arrays will need to be the same size for this to work, so if you have multiple columns in your y array (one column per line) and a vector x, then use repmat(x(:), 1, size(y,2)) as the x for the rotation.

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