Plot polygons as image to process
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Hi guys,
I have data of a curve which I want plot it as an image. And later use function regionprops to get its orientation and centroid.
Is there any way I can do that, or directly get the orientation of the curve data.
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/1304150/image.jpeg)
The image is the polygon plot of the curve, while the data has not duplicate point, the function return:
"Warning: Polyshape has duplicate vertices, intersections, or other inconsistencies that may produce inaccurate or
unexpected results. Input data has been modified to create a well-defined polyshape."
And delete half of my data to draw that image, any suggestion I could do to prevent that?
Thanks!
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Accepted Answer
Simon Chan
on 23 Feb 2023
When you convert the polyshape into an image, the result of the centroid would be different due to the resolution of a pixel on an image.
Regarding to the warning message, you may refer to this: https://www.mathworks.com/matlabcentral/answers/606836-why-does-the-polyshape-function-deletes-the-vertices-in-the-input-when-there-are-no-duplicated-poi
Consider the following example with a very simple polyshape:
pgon = polyshape([20 20 17 15],[7 3 2 9]);
[x,y] = centroid(pgon)
Now, convert it to an image:
A = zeros(25,25);
for k = 1:length(pgon.Vertices)
A(pgon.Vertices(k,2),pgon.Vertices(k,1))=1;
end
J = bwconvhull(A);
regionprops(J,'Centroid','Orientation')
If you want to increase the resolution, for example, 100 times. This would give you a closer value.
MagFactor = 100;
A = zeros(25*MagFactor,25*MagFactor);
for k = 1:length(pgon.Vertices)
A(pgon.Vertices(k,2)*MagFactor,pgon.Vertices(k,1)*MagFactor)=1;
end
J = bwconvhull(A);
stat = regionprops(J,'Centroid','Orientation')
cent = stat.Centroid/MagFactor
figure
ax1 = subplot(1,2,1);
plot(pgon);
axis(ax1,'image');
ax1.XLim = [1 25];
ax1.YLim = [1 25];
ax2 = subplot(1,2,2);
imshow(J);
ax2.YDir='normal';
More Answers (1)
Image Analyst
on 23 Feb 2023
If you have the x and y of the outline, you can use poly2mask to turn it into an image and then use regionprops to get its orientation and centroid.
mask = poly2mask(x, y, rows, columns);
props = regionprops(mask, 'Orientation', 'Centroid');
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