How to calculate Area of overlapping polygons inside square

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cvk engineer
cvk engineer 2020-5-16
评论： darova 2020-5-18
I have requirement to calculate percentage of area covered by polygons inside square(Green Border) for matlab plot.
Logic used is Area coverage= Area of outer square- area of each polygon- polygon overlapping area
I am stuck at finding overlapping area as there are more than 3 polygons overlapping. I am using intersect function for finding intersection
Is there any better method for this requirement(Can Non-plotted are be measured?)

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Steven Lord
Steven Lord 2020-5-16
Take the union of all the polyshape objects representing your polygons
Make a polyshape representing the interior and boundary of your square and intersect that square with the union polyshape.
This results in one final polyshape whose area you can compute.
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Steven Lord
Steven Lord 2020-5-17
The polyshape representing a square and its interior is easy. Here's the unit square.
square = polyshape([0 1 1 0 0], [0 0 1 1 0]);
plot(square)
I'm assuming you want the intersection of the triangles inside the square, not just a measurement of how much of the green line representing the outside of the square covers the triangles. Making that square "annulus" would be a little trickier; there's probably a way to do this using polybuffer but a quick way to do it would be:
figure
square = polyshape([0 1 1 0 0], [0 0 1 1 0]);
w = 0.05;
inner = polyshape([w 1-w 1-w w w], [w w 1-w 1-w w]);
plot(subtract(square, inner))
Change w and recreate the inner polyshape to change how thick or thin the "ring" is.
cvk engineer
cvk engineer 2020-5-18
Issue solved, Thank you so much.
I took union of all the polygons, created polygon of coverage square, got area of intersection of these two..

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darova
darova 2020-5-17
编辑：darova 2020-5-17
What about this simple trick?
I = imread('image.png');
I1 = imcrop(I, [70 75 130 95]);
I2 = im2bw(I1,0.95);
imshowpair(I1,I2,'montage')
sum(~I2(:))
You need only to scale pixels to area
  2 个评论
darova
darova 2020-5-18
Just select region you want
I = imread('image.png');
I1 = im2bw(I1,0.95);
I2 = I1(70:200,75:170);
imshowpair(I1,I2,'montage')
sum(~I2(:))

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