How to calculate Area of overlapping polygons inside square

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?)

Answer 1

[Steven Lord]

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.

[cvk engineer]

Thanks for the quick reply.

I got union of all the polygons with union command.

I am not sure how can i create polyshape for the interior + square border.

I share reference mat file which has coordinates of all the polygons(SensorCovU) and square range(CovCords).

Thanks for your help.

[Steven Lord]

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]

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..

Answer 2

[darova]

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

[cvk engineer]

imcrop needs image processing toolbox which i dont have, thanks.

[darova]

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(:))