Display sum of areas of different categories for multiple polygons in a legend

I have drawn multiple polygons representing different view-out categories, and have calculated the area of each individual polygon. Now i want to display the sum of the areas for each category. I have 7 categories (Other, Sky, Building, Traffic, Car, Ground and Greenery) but many of the polygons belongs to the same category (Building, Car and Greenery).

Is there a way to easily show the sum of the areas for each category in a legend on the plot? If I run the code now, it will just give me the area for each polygon instead of the area for the category, see image below.

figure;
imagesc([-pi, pi], [-1, 1], bg_img);

V = readtable('polygons_brogade_foraar.csv');
V = table2array(V);

hold on;

polygons = {
    'Other',             [-pi 1; -pi -1; pi -1; pi 1], 'white';
    'Sky',               [V(:,1) V(:,2)],              '#4DBEEE';
    'Building 1',        [V(:,3) V(:,4)],              '#A2142F';
    'Building 2',        [V(:,5) V(:,6)],              '#A2142F';
    'Traffic',           [V(:,7) V(:,8)],              '#0072BD';
    'Car 1',             [V(:,9) V(:,10)],             '#EDB120';
    'Car 2',             [V(:,11) V(:,12)],            '#EDB120';
    'Car 3',             [V(:,13) V(:,14)],            '#EDB120';
    'Ground',            [V(:,15) V(:,16)],            '#D95319';
    'Greenery 1',        [V(:,17) V(:,18)],            '#77AC30';
    'Greenery 2',        [V(:,19) V(:,20)],            '#77AC30';
    'Greenery 3',        [V(:,21) V(:,22)],            '#77AC30';
    'Greenery 4',        [V(:,23) V(:,24)],            '#77AC30';
    'Greenery 5',        [V(:,25) V(:,26)],            '#77AC30';
};

Q = polyshape(zeros(0,2));
n = size(polygons, 1);
A = zeros(1, n);
P = cell(1, n);

for k = n:-1:1
    Pk = polyshape(polygons{k, 2});
    A(k) = area(subtract(Pk, Q));
    P{k} = Pk;
    Q = union(Q, Pk);
end

for k = 1:n
    plot(P{k}, 'FaceAlpha', 1, 'FaceColor', polygons{k, 3});
end

for k = 1:n
    fprintf('Addition area polygon %d = %.2f\n', k, A(k));
end

legendStrings = cell(n, 1);
for k = 1:n
    legendStrings{k} = sprintf('%s (Area: %.2f)', polygons{k, 1}, A(k));
end
legend(legendStrings, 'Location', 'best');

axis([-pi, pi, -1, 1]);
xticks(-pi:pi/2:pi);
xticklabels({'-\pi', '-\pi/2', '0', '\pi/2', '\pi'});
title('Region of Interests (ROIs) of the 360° Video');
xlabel('Longitude');
ylabel('Latitude');
ax = gca;
set(ax, 'FontSize', 15, 'FontName', 'Bookman Old Style');

Hope I explained it well enough.

Thank you in advance,

Louis H

Answer 1

[Voss]

figure;
% imagesc([-pi, pi], [-1, 1], bg_img);

% since I don't have your variable bg_img, I set YDir 'reverse' like imagesc does
set(gca(),'YDir','reverse')

V = readtable('polygons_brogade_foraar.csv');
V = table2array(V);

hold on;

polygons = {
    'Other',             [-pi 1; -pi -1; pi -1; pi 1], 'white';
    'Sky',               V(:,[1 2]),              '#4DBEEE';
    'Building 1',        V(:,[3 4]),              '#A2142F';
    'Building 2',        V(:,[5 6]),              '#A2142F';
    'Traffic',           V(:,[7 8]),              '#0072BD';
    'Car 1',             V(:,[9 10]),             '#EDB120';
    'Car 2',             V(:,[11 12]),            '#EDB120';
    'Car 3',             V(:,[13 14]),            '#EDB120';
    'Ground',            V(:,[15 16]),            '#D95319';
    'Greenery 1',        V(:,[17 18]),            '#77AC30';
    'Greenery 2',        V(:,[19 20]),            '#77AC30';
    'Greenery 3',        V(:,[21 22]),            '#77AC30';
    'Greenery 4',        V(:,[23 24]),            '#77AC30';
    'Greenery 5',        V(:,[25 26]),            '#77AC30';
};

Q = polyshape(zeros(0,2));
n = size(polygons, 1);
A = zeros(1, n);
P = cell(1, n);

for k = n:-1:1
    Pk = polyshape(polygons{k, 2});
    A(k) = area(subtract(Pk, Q));
    P{k} = Pk;
    Q = union(Q, Pk);
end

Warning: Boundaries with fewer than 3 points were removed.

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.

Warning: Boundaries with fewer than 3 points were removed.

Warning: Boundaries with fewer than 3 points were removed.

Warning: Boundaries with fewer than 3 points were removed.

Warning: Boundaries with fewer than 3 points were removed.

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.

Warning: Boundaries with fewer than 3 points were removed.

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.

Warning: Boundaries with fewer than 3 points were removed.

Warning: Boundaries with fewer than 3 points were removed.

Warning: Boundaries with fewer than 3 points were removed.

Warning: Boundaries with fewer than 3 points were removed.

Warning: Boundaries with fewer than 3 points were removed.

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.

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.

Warning: Boundaries with fewer than 3 points were removed.

[category_names, h_plot_idx, category_idx] = unique( regexprep( polygons(:,1), ' \d+$', ''), 'stable');

category_sums = splitapply(@sum, A(:), category_idx);

h_plot = zeros(1,n);
for k = 1:n
    h_plot(k) = plot(P{k}, 'FaceAlpha', 1, 'FaceColor', polygons{k, 3});
end

for k = 1:n
    fprintf('Addition area polygon %d = %.2f\n', k, A(k));
end

Addition area polygon 1 = 0.04
Addition area polygon 2 = 4.58
Addition area polygon 3 = 0.77
Addition area polygon 4 = 0.58
Addition area polygon 5 = 0.05
Addition area polygon 6 = 0.00
Addition area polygon 7 = 0.01
Addition area polygon 8 = 0.01
Addition area polygon 9 = 5.97
Addition area polygon 10 = 0.07
Addition area polygon 11 = 0.14
Addition area polygon 12 = 0.15
Addition area polygon 13 = 0.17
Addition area polygon 14 = 0.02

m = numel(category_names);
legendStrings = cell(m, 1);
for k = 1:m
    legendStrings{k} = sprintf('%s (Area: %.2f)', category_names{k}, category_sums(k));
end
legend(h_plot(h_plot_idx), legendStrings, 'Location', 'best');

axis([-pi, pi, -1, 1]);
xticks(-pi:pi/2:pi);
xticklabels({'-\pi', '-\pi/2', '0', '\pi/2', '\pi'});
title('Region of Interests (ROIs) of the 360° Video');
xlabel('Longitude');
ylabel('Latitude');
ax = gca;
set(ax, 'FontSize', 15, 'FontName', 'Bookman Old Style');

[Louis Helledie]

That's exactly what I needed. Thank you so much @Voss!

[Voss]

You're welcome!